Grind is a repetitive, unpleasant, and punishing type of play that a group or single player must overcome in order to access parts of play that they find enjoyable. In tabletop role-playing games, grind is most common in combat, e.g. when it is clear that the party has won a battle but the combat if forced to continue until their enemies have been completely whittled down and finally defeated. Grind is exacerbated by game systems with slow combat systems, and by combat systems in which there is little choice or change over time (i.e. when all characters involved stand around attacking each other over and over again).
Other types of grind exist as well, but are more common in other mediums. Grinding for experience points and treasure is common in computer role-playing games, in which players must repeatedly perform menial tasks (e.g. finding and defeating meaningless enemies) to gain experience or more powerful weapons so that they can take part in gameplay locked to lower-level characters.