Crack in concrete floor slab
This is typical and poses no danger.  It's just a superficial crack in the floor slab.  I suspect if you remove more carpeting, you'll find more.
The biggest concern is that sometimes insects (like ants) can find their way up through these and start invading your home.  I'd seal it with some silicone caulk to prevent insect infiltration.
Other than that, as long as it doesn't start opening up more you should be OK.