In sex, it is feeling or experiencing sexual feelings or attractions towards someone or something.
In sport, it is the intensity of motivation and excitement experienced while engaging in training or participating in sport.
Example One - Sex:
His arousal towards his girlfriend made him further want to make love with her.
Example Two - Sex:
The arousal he felt after watching the pornography made him want to watch more.
Example One - Sport
The footballers' arousal levels were increasing as the match played on, making them further motivated to play well and put more effort in.
What a man feels when he is alternately extremely attracted to a particular woman's unimaginably hot body but also completely disgusted by her unimaginably ugly face. This generally produces disorientation in the first few episodes but can sometimeslater reshape sexual attraction as the ugly face becomes a fetish of sorts.
"Hey Jake, check out the smoking hot babe walking down the beach."
(Moments later) "Hey baby. my name's Tony." (She turns around and Tony almost throws up. She walks away only to appear smoking hot again. The arousal repulsion cycling continues on like this all day long.)