A personal foul is any violation of the rules of the game that involves personal contact with an opposing player. This includes hitting a player while they are shooting the ball, impeding the path of a player while they are dribbling the ball, hitting the arms or body of an opponent in an attempt to steal the ball, and many other violations.
In the NBA, once a player commits his sixth personal foul in a single game, they have fouled out and are not allowed to play for the remainder of the game.
When a defender fouls a player that is shooting the ball, that is called a shooting foul and free throws are given to the player that was fouled. If the shooter makes the shot while being fouled, they receive one free throw in addition to the basket counting. If the shooter misses the shot while being fouled, they receive either two or three free throws depending on whether the shot attempt was a two-point shot or three-point shot.