[yef]

Language is not precise, and companies define their roles differently for a variety of reasons, including the nature of the business each company is in. I'll take a stab though.

In general, "salesperson" implies a single transaction. You go to the Apple Store, you talk to a salesperson, you walk out with a big iPhone and a light wallet. Note that Apple calls them "specialist" or something, see point above.

"Account" implies an ongoing relationship with a steady stream of transactions, such as an advertiser with a large account on an ad platform. The account manager's role would be a) make sure to keep the account and b) find ways for the account to spend more money in a way that's beneficial to both.

Account executives typically sign new accounts, so they are overall selling the value of the ongoing stream of transactions.

Further muddying the waters is that all these roles are under the "Sales" org, so you could arguably say an account manager is in sales even if they're not a salesperson you meet at a retail store.