Custom control is a control that is not included in the .NET framework library and is instead created by a third-party software vendor or a user.

Custom control is a concept used while building both Windows Forms client and ASP.NET Web applications. Custom client controls are used in Windows Forms applications, while custom server controls are used in ASP.NET pages (Web forms). Using custom controls is easier in .NET than the earlier Windows versions due to simple programming techniques.

Custom control is a generic term that also includes user controls. User control in ASP.NET is created using ASP.NET code and is reused in other Web pages, whereas user control in the context of Windows Forms implies a composite control with a consistent user interface (UI) and behavior within or across applications.