If you bought it in Florida (the land of "it's what we call it", it is a Japonese Sambokan... one of the key ingredients in Japonese lemon flavored soy sauce.

Thank you John. I bought it in Canada. Last winter. Do I keep it till it yellows or it is ready now?

Probably ready now; but all limes/lemons will get a bit yellow if you leave them on the tree; and most are better when they begin to get a little yellow.