Fair territory in baseball refers to the area in which play is legal and fair. Within baseball, there are two areas to be aware of, fair territory and foul territory. Most of the time, these two terms are used when referring to foul balls, and where the ball lands on the field.
The foul lines determine where fair and foul territory are situated. Fair territory is contained within the foul lines, whilst foul territory is situated outside the foul lines. A ball which lands outside of the fair territory is known as a foul ball.