This is slang, but not very commonly used. It means to work really hard at something. For instance working hard every day in a terrible job is" your daily grind." Or instead of "rise and shine" which means to get out of bed with a positive attitude, someone might say "rise and grind" , meaning to get up and get right to work at a difficult job.

Interesting question! We use to grind

Yes, people talk about the grind in War Thunder . . . It means if have to play a lot with low level weapons, etc. before you earn enough points to get the better items. Grind is used in general for long term work. Some people refer to having to work as the 'daily grind.'

Yes, its commonly used in games, especially RPGs. "I'm grinding for X item" "I'm grinding for 5 levels" They all mean that what you are trying to acquire is difficult or rare.

Thanks guys for giving me a new word.