What is a window breaker (AKA glass breaker)?

It’s a thick tip of steel—usually pointed—on the back of your handle that’s meant to break glass or a window in an emergency. The hardened steel spike will be much more effective striking, rather than stabbing the glass with the knife tip. Also, they just look slick. Window breakers can be hand crafted if you so choose.

Also seen in the picture is a seatbelt cutter (generally considered redundant). Source.