What is considered self-harm?

Does self-harm have to be cutting, burning, drinking poison, etc? (I know that there are many types of SH but I'm just wondering if I'm struggling with it or not.)

Many people use rubber bands to get clean and get the bad thoughts to dissapear (not only with SH, much more too) but I use that as SH. I pull it around my wrist twice and sometimes it leaves marks. The marks usually fade eventually, I have one that I got from one time when I had it pulled around my wrist like that for several days (maybe 4 or something idk), but it has faded and you can barely see it at all.

I was also wondering, if this is self-harm, does that mean while I have it tightly wrapped around the wrist, I'm self harming at the moment?

It's probably very confusing and I wouldn't like to think it's that common or that barely anyone SH in this way, or whatever you can call it.