What are Braxton Hicks?

Can someone please explain them to me. I’m not sure if it’s what I’m having or it’s just other pregnancy symptoms.. I’m 17 weeks by the way.

Basically I woke up this morning and my stomach was reeeaaally hard. And it was harder on the right than on the left. I had a totally full bladder and was a little crampy. Also, whenever I let some gas out in the morning it’s kinda painful...

I laid back down to see if my stomach was still had after using the bathroom and it wasnt. Just the typical sorta hard from being pregnant if that makes sense.

Through out the day I’ll get cramps feelings either on my left or right side, more so On the side of my stomach but I think that’s just round ligament pain.

Any help would be appreciated !