14 English words students learn differently if their teacher is American vs. British
When a chip isn't a chip and a flapjack isn't a flapjack.
Flapjacks in the U.S. are something totally different than flapjacks in the U.K.
Even though Americans and British people technically speak the same language, there are some major differences in our English vernacular. For instance, if you were to give someone from the United States and someone from England this prompt:
Draw a kid in a jumper eating chips, biscuits, and flapjacks while watching football.
You would end up with two very different drawings. The words jumper, chips, biscuits, flapjacks, and football all have completely different meanings in American English vs. British English. Most of us know the football vs. soccer difference, but the others may be unfamiliar.

Words in the same language having different meanings based on geography can be confusing for English language learners, especially when they're learning how to order food in a restaurant. Here are some differences just with foods alone:
Chips
In the U.S., chips means potato chips. As in Lay's, Ruffles, etc. In the U.K., those are called "crisps," while chips means french fries. Hence fish and chips meaning fish and fries, not fish and Ruffles.
Biscuits
When Americans talk about biscuits, we're talking about fluffy, flaky baked balls of dough smothered in butter and served with either soups or meat and mashed potatoes, generally. Buttermilk biscuits are an American staple. Not so in the U.K. where a biscuit simply means "cookie." What we call a biscuit, they call a scone. We have scones in the U.S., too, but our definition is generally more limited to the triangular, sweet kind. British scones also cover what we think of as biscuits.

Flapjacks
A flapjack in the U.S. is synonymous with pancake—the breakfast staple. A flapjack in the U.K. is a baked oat bar, almost like a granola bar.
Pudding
If you order a sticky toffee pudding in the U.K. and expect to get a custard-like substance, you'd be disappointed. Pudding is a general term for a dessert in the U.K., whereas it specifically means a custard dessert in the U.S.

There's also the opposite issue, where we use different words for the same foods as opposed to the same words for different foods. In the U.K., a zucchini is a courgette, an eggplant is an aubergine, cilantro is coriander, a grilled cheese sandwich is a toastie, and Jell-O is jelly.
Clothing also can be confusing for folks learning English from an American vs. a Brit. Here are some words:
Jumper vs. Sweater
In the U.K., a jumper is what we call a sweater. In the U.S. a jumper is kind of like a mix between overalls and a dress—a sleeveless garment generally worn over something else.
Pants vs. Underpants vs. Trousers
What Americans call pants, folks in the U.K. call trousers. (Americans know the word trousers, but we don't use it much.)

Vest vs. Waistcoat vs. Undershirt
This one is super counterintuitive for Americans. A "vest" in the U.K. is an undershirt, like a thin t-shirt or tank top. What Americans think of as a vest, the Brits call a waistcoat.
Braces vs. Suspenders
This one is also counterintuitive for Americans. For us, braces are either the orthodontia that straightens our teeth or a supportive apparatus that stabilizes a body part (a leg brace, wrist brace, etc.). But braces in the U.K. has another meaning, which is what we call suspenders. In the U.K., suspenders don't hold up pants—those are braces—but they do hold up stockings, which isn't the way we use that word.
Bonnet and Boot
A bonnet is a head covering in both the U.S. and the U.K., but the Brits also use the word for the hood of a car. Boots are shoes that go above the ankle in both countries, but a boot is also the trunk of a car in the U.K.
That's not the end of the list of words that differ between American English and British English, but it's a good start. For folks learning English as a second language, it's at least good to know that some things you learn will really depend on where your teacher is from so you don't end up disappointed when you order pudding or biscuits at a restaurant and get something totally different.
