Looping is just the repetition of small bits of sound, somehow manipulating that sound and then playing live music over the top. The original version used magnetic tape actually taped together to form a loop. These days, it is done digitally, with loopers able to record up to several hours of material.
I originally got into looping from incorrectly hooking up a reel to reel recorder, feeding the output back into the input, when I was about 12. It repeated, and got louder, and more compressed, and smeared into this wall of sound with every note I played. At this point, as a guitarist I had never heard of Robert Fripp, much less his Frippertronic tape-loop system. It amazed me to find out someone had made recordings of this stuff.
Later on, I discovered Fripp & Eno’s ‘No Pussyfooting’ on tape. Then Fripp’s ‘Let the Power Fall’, and eventually my favorite looping recording, Brian Eno’s ‘Discreet Music’.