From WHMCS Documentation

Glossary of Terms

This section will attempt to clarify what is meant by terms used in WHMCS and the documentation.

3D Secure

3D Secure is an extra step in the payment process, known to consumers as Verified by Visa of Mastercard Securecode, whereby they are directed to their bank to enter a password to verify the payment. If a payment gateway does not support this option, clients will never be prompted to provide their 3D Secure password.


An array is a special variable which can hold many values under a single name, and you can access the values by referring to an index number.


An acronym of Application Programming Interface, specifies how two pieces of software communicate. For example WHMCS uses the eNom API to community domain registration requests to eNom. The WHMCS software has its own API that in turn allows other pieces of software to perform actions in WHMCS remotely.


A Boolean data type is a data type with only two possible values: true or false.

Billing Cycle

The frequency with which a service will generate invoices, such as monthly, semi-annually and annually.


See #Defect

Change Package

The module change package function is the process by which WHMCS sends the signal to the server/service telling it to change the client's package (ie. upgrade or downgrade). If the configurable package addon is in use for the product, this option can also be used to change the client's individual quotas in the configurable options.

Client Area Link

This module feature will display a link on the product details page in the WHMCS client area which clients can click to login to the server control panel.

Configurable Option

Allows for the customisation of products within set parameters. Typically used to allow clients to choose certain aspects of their hosting product (disk space, bandwidth). Always takes the same billing cycle as the service.


The module creation function is the process by which WHMCS sends the signal to the server/service telling it to create the necessary account. The credentials entered under the client's Products/Services tab are often passed to the server/service within the command, at a minimum typically the username, password and domain.


A cron is a time-based job scheduler in Unix-Based systems. WHMCS makes use of this system to trigger a number of the automated tasks, including invoice generation, overdue reminders, suspension, termination, ticket escalation rules and more.

Cron may also be used to refer to the specific script which should be triggered by the server's cron scheduler this is located at /crons/cron.php

Daily Tasks

Daily Tasks are specific actions which WHMCS performs only once per day. For example sending overdue reminder emails are considered a daily task because they are sent once per day, but escalation rules are run many times per day, so are not.


A number with decimal amounts. Mostly with two decimal places, but in some situations can have more. xx.xx


A defect in the WHMCS software occurs when the actual behaviour of a specific part or function operates otherwise in accordance with the intended design. This is distinct from the desired design of an end user. The decision as to what constitutes intended design and a defect lies with WHMCS personnel.

Reproducible defect reports in the stock software are welcomed at
Proposals for changes to the intended design can be submitted for consideration at


An email address formatted with an @ symbol

First Payment Amount

When Next Due Date = Registration Date, this value will be the amount the client is initially invoiced for their service. It is the sum of the product Setup Fee + Price + configurable options.


An integer is a number that is written without a fractional component. For example, 21, 4, and −2048 are integers; 9.75, 5½, and √2 are not integers. The set of integers consists of the natural numbers (1, 2, 3, ...), zero (0) and the opposites of the natural numbers (−1, −2, −3, ..., that are negative).


Json is an open standard format that uses human-readable text to transmit data objects consisting of attribute–value pairs. It is used primarily to transmit data between a server and web application, as an alternative to XML.

Menu Items

Menu Item Class

Menu item objects are the core building block to all programmable client area menus in WHMCS. They power dynamic navigation bars, sidebars, the client area home page's panels, and other UI elements. Individual menu items contain all of the components necessary to render it on a page including display labels, links, icons, and certain HTML elements.

Menu items are arranged in a tree structure. A menu item can have many child items and one parent item. The only item with no parent is the root menu item at the top of the tree. The root menu item has access to every child item in the menu tree.


A file which contains the code that communicates between WHMCS and provider's API. For example the cPanel module contras the code to communicate with the cPanel API. The eNom module contains the code to communicate with the eNom API and so on. Comes in three types; provisioning, registrar and gateway.

Next Due Date

The date at which the client's next renewal payment is due. Invoices are typically generated several days in advance based upon your Automation Settings. It will automatically increment forward one billing cycle when a renewal invoice is paid.


An item that can be purchased by a client via the order form. Usually with a fixed price although they can be customised via configurable options and product addons. These are configured in the administration area under Setup > Products/Services > Products/Services.

Product Addon

Can be added on to a product to increase the price. Usually one-time or recurring items that you may wish to upsell to clients such as a software licence. They should be considered on/off options and can have a separate billing cycle as the service.

Recurring Amount

Provided Next Due Date =/= Registration Date, this value will be the amount the client is invoiced for the next renewal of their service. It is the sum of the product Price + configurable options.


The 'Sandbox' is a development system that enables you to test your checkout for functionality without being 'live' so any transactions you use to test it are not 'real'. When you are happy that everything is working properly just deselect that option.

Standard Hook

A standard hook is determined within WHMCS to be a hook that runs when a specific action occurs. A return may be accepted, see the hook page for more information, but no validation occurs on the hook return.


When a client orders a Product, that particular instance is referred to as a Service. The Service record can be accessed from the client's Products/Services tab and can be customised form the default price, billing cycle, addons can be added and configurable options can be changed.


A string is generally understood as a data type and is often implemented as an array of bytes (or words) that stores a sequence of elements, typically characters, using some character encoding. A string may also denote more general arrays or other sequence (or list) data types and structures.


The module suspension function is the process by which WHMCS sends the signal to the server/service telling it to suspend the account on the server. Typically the client files and setting will be retained but access to their account on the server is blocked.


We regular expression match/validate a single digit, a space, a dot, a dash or a pair of brackets. Instead of making sure the whole string matches a string of correct characters, we replace all correct characters with empty strings, and whatever is left behind is assumed to be wrong and will fail validation.

A standard phone number, in local format, without any country code.

International Telephone

An automatically formatted number using the client country to add the country code. In the format +CC.xxxxxxxxx


The module termination function is the process by which WHMCS sends the signal to the server/service telling it to delete the account from the server. The record of the account will remain within WHMCS.


The module unsuspension function is the process by which WHMCS sends the signal to the server/service telling it to reverse the suspension process and re-activate a previous suspended account on the server.

Usage Updates

If enabled in Automation Settings this module feature enabled WHMCS to obtain the disk space and bandwidth usage for individual accounts. This is displayed in the client and admin areas and can be used on conjunction with overage billing.

Validation Hook

A hook that runs to perform a validation check on the data being entered. The return from this hook can stop the saving of data from occurring. See the hook page for more information.