Basic economy is the airline's cheapest fare on a flight most people are already booking, sold by taking a normal ticket and removing things until the price drops. You sit in the same cabin, in a seat that's often identical to the one next to it, on the same plane, at the same time. What changed is everything around the seat: when you board, whether you get to choose where you sit, what you can bring, and how much it costs you if your plans move. The fare is real and it can be a genuine deal. It's also the easiest ticket to buy without realizing what you agreed to.
What actually gets removed
The restrictions vary by airline, but the pattern is consistent. You usually board last, which on a full flight means the overhead bins are gone and your carry-on gets checked at the gate anyway. You often can't pick a seat in advance, so if you're traveling with someone you may end up rows apart unless you pay to sit together. Some airlines limit you to a personal item and charge for a normal carry-on. And the ticket is typically locked: no changes, no cancellations for credit, or a fee steep enough to erase what you saved.
None of that is a scam. It's an unbundling. The airline pulled the perks out of the fare and is selling them back one at a time. The problem is that the perks you'll want are easy to guess in advance, and once you add them back the "cheap" fare often lands right next to the standard one you skipped. That's the same trap we wrote about in the hidden cost of a cheap fare: the sticker is the start of the bill, not the end.
When it's actually the right call
Basic economy earns its price for a specific trip. You're flying light with a bag that fits under the seat. Your dates are fixed and you're confident they'll hold. You don't care where you sit or when you board. A weekend trip with a backpack is the clean case: nothing you'd pay extra for, so nothing lost by skipping it. If any of that isn't true, price out the standard fare before you decide, because the gap is often smaller than it looks.
We're not going to tell you which fare to buy, because it depends on the trip only you know about. What we do is send a few real options side by side every morning, so the cheapest line isn't the only one you see. Sometimes the fare a few dollars up already includes the seat and the bag you were about to pay for. Read past the first number, the way you would for anything else worth checking before you book.