Grind
Grind is the process required to increase a game character's level, experience, or ability. It gets its name "grind" because it's a repetitive task and may start to feel more like work instead of a game.
Grinding is common in MMORPG (massively-multiplayer online role-playing game) when leveling, looking for a unique item, or need to complete a quest that requires many kills.
What is a grindwall?
The term grindwall describes grinding for something (e.g., special item) that requires a lot of killing of the same mob or boss to acquire. Sometimes an F2P (free-to-play) or P2W (pay-to-win) game purposefully adds a grindwall to help entice players into paying real money for the item or make it easier (convenient) to acquire.
In other words, an F2P game may be free because many of the items and achievements require an excess amount of grinding. However, someone paying a monthly fee may have convenience features that allow them to avoid the tedious grinding.