The noun rejection can refer to the actual act of rejecting something or to the feeling one has after being rejected. In other words, you might have feelings of rejection after experiencing the rejection of others.
The Latin noun rēicere, which means "to throw back," is the ancestor of the word rejection. Nobody likes to feel the rejection of being excluded. The word rejection became popular in psychology in 1931, when parental rejection was seen as a motivation of bad behavior in children. The word found a medical meaning by 1943, as the body's refusal to accept a transplant.