Program which is responsible for preparing and launching a process.
When the application is launched, the operating system loader reads the disk image of the app, parses the structure of it, prepares it into memory, and then passes control to the processes entrypoint.
Commonly used to describe a program which performs a memory patch of an application, in order to remove the protection.
This kind of loader launches the target, waits for a delay or predetermined condition to occur, and then applies a patch to the processes code.