Grind is repetition. Simple enough.
But do we always see it?
Let's take a look at some types.
1. Item degradation; this is the need to replace powerful items, by either repeating content or paying some other price.
An example would be Dungeoneering weapons, needing gold or tokens to repair/replace the item.
2. Training skills. Repeat actions until you unlock other actions you can repeat that give faster experience so that you can repeat them less often until you have maxed out and can no longer repeat the action. At which point you have completed the content and can leave the game.
In Runescape we live in a world of fantasy, where work is rewarded equally and fairly. This is part of the appeal of Runescape. That everyone is equal and that everyone can choose whichever path they want. Including not grinding.
3. Boss killing. Players aim to kill as many bosses as possible per visit. The reward is more profit per dungeon run. More efficiency. Players actively work to make bosses a grind, to make them an efficient little slaughterhouse. This is one reason why companies like Jagex start thinking players love grind. And design rewards for it.
4. Champion scrolls are a reward for grinding. Basically you kill about 10,000 of one type of monster and then hope for a scroll to drop, and then do it for other monster types that are all easy to kill. But grindy.
5. Bots are a player reaction to grind. Bots are automated scripts that do all the boring work for you, they can farm experience and/or gold while you sleep, or play more interesting games.
6. Prestiges. This is one of those words that means something different from its dictionary definition. In Runescape it was to be an indication of how well you could grind, in fact it still is. Prestige in Dungeoneering is the method the players have to use to keep track of their grind progress and to make sure they grind efficiently.
Prestige was also a proposal to get players to completely rework entire skills, and was greeted with derision and once put to a poll, voted out. Basically it was a lazy development idea. Instead of Runecrafting 99, you would get Runecrafting 99 (2) and some sort of cosmetic reward that nobody would recognise, because Runescape is full of random cosmetic rewards from the pay-to-win options in the game.
7. 2007scape. This was a Runescape update to give players a chance to start again. To do over what had been undone. Partly a response to player demand for older servers for their different rulesets and partly created as an escape from some highly unpopular updates. It's proving somewhat successful with about one third of paying members using that game version.
That's not all!
I kid. Just marketing you. You can relax.
But there is more.
Too much to bore you with.