What constitutes cheating to you? {Possibly NSFW}?

Everyone feels differently about what cheating is when it comes to relationships. Personally I feel even talking to someone in a sexual manner is cheating. Even just talking to a person besides your S/O about important things in your life can be considered cheating. Confiding in someone else besides your S/O could be cheating.

Oral sex?
Mutual masturbation?
Sex with a member of the same sex when your in a straight relationship?
Phone sex?

What do you consider cheating?