What is multi tasking, multi programming, multi threading?

All of these are computer related processing abilities.

Multitasking is the ability of an OS simultaneously to execute more than one task on single processor.

Multiprogramming is also the ability of of an OS to execute more than one programme on a single processor.

Multithreading is the ability of an operating system to execute  to execute  the different parts of a Programme called Threads at the same time.