DLL stands for “Dynamic Link Library”, an implementation of the shared library concept in Windows.
A DLL (.dll) file contains a library of functions and other information that can be accessed by a Windows program.
There are several common functions used by programs. For example, many programs such as .exe files allow users to open and save files.
The code for these functions could be added to each program separately. However, a more efficient method is to have a common file (or library) containing these functions to be used by any program that needs them.
That’s what a .dll file – in the above example the COMCTL32.dll file – does. DLL files sit on a Windows machine ready to be used when required.
Note that .dll files can’t be run on their own; they require an executable program.
Here’s a more comprehensive definition from the techterms website:
A DLL (.dll) file contains a library of functions and other information that can be accessed by a Windows program. When a program is launched, links to the necessary .dll files are created. If a static link is created, the .dll files will be in use as long as the program is active. If a dynamic link is created, the .dll files will only be used when needed. Dynamic links help programs use resources, such as memory and hard drive space, more efficiently.https://techterms.com/definition/dll
It’s possible to check, and fix, DLL errors using WinThruster by Solvusoft.