In basketball jargon, the "elbow" is the point on both sides of the court where the free throw line meets the edge of the key.
The term "elbow" is typically used to describe a spot where a player receives an entry pass. The "elbow" compares to the "post," which is also along the edge of the key but much closer to the basket, and the "wing," which is a spot on either side of the court where the invisible line created by extending the free throw line meets the three point line.