Stop in for a cup of coffee
Fluke. Closely related.
All fluke are flounders, but not all flounders are fluke.
Generally speaking, left-side up flounder are flukes, and right-side up are called flounders.
You tell by looking down the dorsal fin into the belly (lower jaw) and the side that has the eyes determines which it is. On the left is a fluke, on the right is a flounder.