This is a foul called on the defensive player when that player illegally impedes the progress of the offensive player with the ball.
In the NBA, there is a semi-circular area immediately beneath the rim where blocking and charging fouls are not called. Outside this area, a defender must be in a legal defensive position before the offensive player gets to them in order to draw a charge on the offensive player. If the defender does not get into position before the offensive player gets there and contact is made, a blocking foul may be called. This foul is called subjectively based on the amount of contact and how much the defender impedes the offensive player. A rule of thumb is that if the defender sets their feet prior to absorbing contact from the offensive player, a charge will be called. If the defender has not set their feet by the time contact occurs, a blocking foul will be called on the defensive player.