4. Hold it: used if you were being asked to wait. Think of the start if a race, instead of "on your marks, get set" you could say "hold it, hold it"

5. Hold up: Used in the same way as wait up...more regional. So where I'm from in the North (Yorkshire) we say "'Old up" dropping the h. To get someone to slow down or wait.

Hope that helps!

As with a lot of English phrases it does depends on situations. Hope these help.

1. Wait: I'd use this as a direct order, with my students/children for example when they are crossing a road.

2. Wait up: this is more informal, so if I was with my friends and they were walking too fast I might say "wait up" for them to slow down.

3. Hold on: Used in conversation, perhaps if you were being accused of something or wanted something explained in more detail. For example: "I'm arresting you for murder" you might say "hold on, what do you mean?" It seeks further explanation.

My daughter, 15, uses "wait" as a temporiser, a thing to say while she thinks what she wants to say, wait, what she's going to say, wait, no, what she wants to say. :)