According to a history documentary this blogger remembers watching some time back, 'the daily grind' was originally a literal grind; the processing of cultivated grain to make flour for bread, which people would do on small stone wheels. In their thatch roof cottages. Before the Trogdor came in the niiiiight.
But in the context of MMOs, such as Scott Jennings' recent criticism of Warhammer Online for being grindy, what exactly makes a grind? It's easy to come up with a rough definition: doing the same thing over and over with little variation and modest but predictable reward, a bit like grinding little stone wheels to make enough flour for one family sized loaf.
However, given that pretty much everything you do in an MMO is a task carried out for some sort of reward or other, what stops it all from feeling like one big grind - variations in quest type, changes of scenery, or changes of mob type? What features work best - and worst - to break up the monotony? What makes the difference between feeling like you're playing and feeling like you're grinding?