7.62x51mm NATO and .308 Winchester are essentially the same cartridge. [0] It's basically the same situation as 5.56×45mm NATO vs .223 Remington.

There's a lot of ~7.62mm cartridges out there, as a carryover from when people used imperial units. (It's basically .30 inches) [1]

0: https://www.shootingillustrated.com/articles/2018/8/19/308-w...

1: https://en.wikipedia.org/wiki/7.62_mm_caliber

As a note when most people say 7.62 it is generally short hand for saying 7.62 NATO. They usually specify if it is one of the other 7.62 rounds. As well the .308 is a similarly cartridge round and 7.62 NATO rounds can be shot from a .308 gun but 7.62 NATO guns should not be used to shoot .308 rounds as the .308 has a slightly higher chamber pressure.