To expand on the Translator's note here: "Choking up" a bat means to place your hands further up the bat than normal. This causes you to swing the bat through the zone faster, giving you a split second of additional time to make contact with a fastball, which can be all the difference. You sacrifice a lot of power the more you choke up on the bat, though.
Pictured: Cincinnati Reds 1st baseman Joey Votto, famed from nearly always choking up on the bat. Notice his hand placement.
Here's an article that goes in depth on the physics of choking up:
https://tht.fangraphs.com/the-physics-of-choking-up/