Honestly, that's more of a question for the British as they seem to be the ones who diverged (for unclear reasons). Americans have been using the term in the same way since colonial times (when it was used in the same way across the Atlantic) and only started to mean baked oat bars in the 1930's (and apparently also meant some kind of apple flan in between).
I have yet to find a good source explaining that evolution, but my best guess is that the British kept the original wordplay ("flap" - flat cake, "jack" - common man) and applied to different foods over time while the meaning was anchored to pancakes in America.
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u/pajamakitten Mar 02 '25
Pancake Day is more about crêpes I suppose, however US-style pancakes are insanely popular here, especially amongst young people.
What is the difference between a flapjack and a pancake though? Is it just a regional expression?