An embed is any piece of hardware cast into the concrete rather than added later: a steel plate, a threaded insert, a lifting anchor, or a connection angle. It is set in the mold before the pour and becomes permanently part of the piece.
Embeds carry the loads that matter most. Lifting anchors let the crew pick the piece safely, and connection embeds tie one piece to the next in the structure. Because you cannot move them once the concrete sets, their exact location on the shop drawing has to be right the first time.