.DLL (Dynamic Link Library) files are components of the Windows operating system. These DLL files enhance the efficiency of software applications and the operating system by providing shared access to a common set of functions. Instead of every application having its own copy of every function, common functions are kept in these DLL files so they can be shared among many applications. If a DLL file becomes corrupted or goes missing, it can cause errors or issues with any program that relies on it.
Some software patches work by replacing or modifying DLL files. This way, the main executable remains unchanged, but the behavior can be adjusted by altering the DLL.