The elbow — the joint (or the area) between the upper arm and the forearm.
テーブルに肘をつかないでください。
Please don't rest your elbows on the table.
転んで肘をすりむいた。
I fell and grazed my elbow.
野球で投げるとき、肘を痛める選手が多い。
Many players injure their elbows when pitching in baseball.