It seems like we're almost all agreeing here haha
Anything that goes against what you've agreed upon in the relationship is cheating. If you're going behind your partner's back/keeping them in the dark then it's cheating. Course this is all variable from relationship to relationship. I mean, my guy is completely fine with me dancing with other guys and girls when I go to the bars and he doesn't come with me. I know couples who would break up if their SO did this because they'd think it's cheating.
Relationships are trust, compromise, and agreements about boundaries. If you violate a boundary it doesn't mater what gender you're doing it with (unless your SO honestly believes that's not so and has clarified that with you).