Do you know what a jump stop is, let alone what is a legal jump or illegal jump stop is?.
A player may gather the dribble in while in the air or one foot on the floor or receives a pass in the air may land on both feet at the same time and then they may either pivot, take off for a shot off the pivot foot or dribble (if they received the ball in the air on a pass). This is a legal jump stop which allows them to pivot or leave the floor off one foot to shoot the ball on the move off the pivot foot. This move is like jumping in the air to get a rebound or jumping in the air to receive a high pass. You may land on the floor, pivot and dribble or just start your dribble.
If a player with the ball takes off on one foot on the move and lands on both feet the player may lift one foot to pass or shoot. If the foot returns to the floor before the player releases the ball, then that is an illegal jump stop and traveling is the correct call.
It is very hard to make a legal jump stop when dribbling in the free throw lane with a person guarding you on the dribble and with help defenders on either side of you.