a hollow point is also known as an "armor piercing round", it will go through a Kevlar vest like it is made of tissue paper. Meaning it is specifically designed to kill armed adversaries, so it is often used by the military.
a hollow point is meant for more damage and less penetration. when it hits a target, it expands and does more damage as it goes further in the target. but when it exits, it takes some of the target with it.
Regular "Ball" ammunition is solid and will generally pass through a body.
Hollow Points are constructed to facilitate mushrooming, or opening/flattening out, so that all of the "Hydrostatic shock" of the round is expended inside the body cavity to cause as much damage as possible.