What is lightening crotch? And how do I know if I have Braxton Hicks (and it’s not just baby’s position)?

I know this sounds stupid but I’m almost 35 weeks and have heard the term ‘lightening crotch’ but have no idea what it is or what it feels like?

I know BH feels like a tightening in your tummy, but mine often feels tight when baby moves position and pushes out. How do I know the difference between baby’s position making me feel tight or BH?

Sorry if it sounds dumb! I’m a FTM so this is all new to me!