What is a pump? First you need to know that the term pump is referred to as the effect on your muscles after working them out. When you work out, the muscle fibers have micro tears causing your muscles to swell a little, drawing more blood into the muscles, making them expand to deal with excess fluid. This has the effect of creating the appearance of yourself being a bit more muscular and vascular.  It lasts about 2-3 hours after a good workout, leaving your muscles in an anabolic state.( Anabolic state is when your muscles are in need of energy and proteins and is the prime time to protein. ) Fun fact: that’s where the term “swole” came from and now you know what a pump is. ( Swole is the term commonly used now to refer to muscles right after a good workout. )