The only silly question is the one you don't ask
Simple and fast. Cat, apple, banana, goat....especially if you are doing word cards.
I suppose if you are doing picture cards for encyclopedic knowledge you could say "this is a cat" but the kids will get bored hearing it over and over, they just want the essential information fast (usually).
I wouldn't use " this means" as it's to ambiguous. Clear and consice is best in life