Most RPG games have a system to measure strength and knowledge which is also referred to as levels. A character will usually start out at level 1. Once he gains enough experience points (or EXP) through the game he will be granted an additional level making him level 2 and so on. This increase in level is referred to as leveling up or the short version lvl up. In addition to being a form of measurement, levels increase stats like hit points or strength points rewarding the player and opening up the use of equipment or difficult parts of the game that they were previously unable to survive in. This leveling can carry on until they reach max level which most of the time is at level 99. The leveling system is one that is always represented by a number.
Unlike levels, as in stages, or courses, levels in RPGs are dependant on the player's past actions, but not necessarily narrative progress. In some cases a player can level up to the highest possible level at the earliest point in the game where EXP becomes available. But typically, the player will gain very low amounts of EXP from monsters in earlier areas of the game, and higher EXP from monsters later in the game. The amount of EXP required to level up tends to adjust accordingly. Ideally, if the player plays the game at a smooth pace, they'll level up at a smooth pace. As a result if they lag behind they'll level up more slowly (some times ridiculously slow) and if they skip ahead they'll level up more quickly.