Retainer clip. Could be fender liner, bumpers or splash shield under the engine.

 

is it a big deal or nah?

 

Nah...unless you find a lot of them all at once or something.

 

My one fender liner is missing 4/5 clips on it. I wouldn't be too concerned.

 

I bought a pack of these and tend to replace loose and missing ones whenever I come across them while working on the car.

 

Nissan p/n: 01553-2DR9A (Clip- Trim, Push Pull). A 10-pack of OEM will run ≈$5-10 though generic options are available. They are a dime a dozen (figuratively, not literally) on Amazon or eBay.

Half of the car is held together with these clips and 10mm bolts. I, also, keep a bag or two on hand as they always break.

 

This looks like something fixed.