In many RPGs, characters start as fairly weak and untrained. When a sufficient amount of experience is obtained, the character "levels up", or gains a superior level. Such an event usually increases the character's statistics, such as health points and strength, and may permit the character to acquire new abilities or improve existing ones.
In some (usually Dungeons & Dragons-derived) games, experience points are used to improve characters in discrete experience levels; in other games, such as GURPS and the World of Darkness games, experience points are spent on specific abilities or attributes chosen by the player.
In most games, as the difficulty of the challenge increases, the experience rewarded for overcoming it also increases. As players gain more experience points, the amount of experience needed to gain new abilities typically increases. Other games (mostly video games) produce a similar effect in a different way, by keeping the amount of experience points per level constant, but progressively lowering the experience gained for the same tasks as the character's level increases. Thus, as the player character strengthens from gaining experience, they are encouraged to accept tasks that are commensurate with their improved abilities in order to advance.
Typically levels are associated with a character class, and many systems will allow combinations of classes, allowing a player to customize how their character develops.
Experience levels fell out of vogue during the late 1980s and most of the 1990s, but began to come back with the 2000 release of D&D 3rd Edition and the d20 System. Some systems that use a level-based experience system also incorporate the ability to purchase specific traits with a set amount of experience; for example, D&D 3rd Edition bases the creation of magical items around a system of experience expenditure (known as burning xp) and also uses a system of feat selection which closely matches the advantages of systems such as GURPS or the Hero System. The d20 system also introduced the concept of prestige classes which bundle sets of mechanics, character development and requirements into a package which can be "leveled" like an ordinary class.
In many games, characters must obtain a minimum level to perform certain actions, such as wielding a particular weapon, entering a restricted area, or earning the respect of a non-player character. Some games use a system of "character levels", where higher-level characters hold an absolute advantage over those of lower level. In these games, statistical character management is usually kept to a minimum. Other games use a system of "skill levels" to measure advantages in terms of specific aptitudes, such as weapon handling, spell-casting proficiency, and stealthiness. These games allow the players to customize their characters to a greater extent.
Some games, notably multi-user dungeons (MUDs) and massively multi-player online RPGs (MMORPGs), place a limit on the experience a character gains from a single encounter or challenge, to reduce the effectiveness of power-leveling.
Remorting is another technique that, while encouraging power-leveling, alleviates its ill effects by giving the player a sense of achievement as it maintains balance with other characters of lower level within the game.
The term's origins are unclear but are thought to distinguish re-mortals (reborn characters) from mortals (normal characters) and immortals (game administrators). An alternate explanation comes from MUDs, in which players may apply to become immortal characters who tend to a game's administrative issues, development, or design. Administrators are generally expected to distance themselves from gameplay; interaction with other players may be severely limited. When an administrator chooses to vacate his or her position to resume playing the game—usually from level one just as with any new character—he or she is said to have remorted.
Power-leveling can mean different things depending on whether or not other people are playing the game. Sometimes in single-player games it refers to a player strategically playing with the sole intent of gaining experience points as quickly as possible. This is frequently done by finding opponents that give a lot of experience points for very little challenge or by going to an area with very powerful monsters and making great use of the game's healing system. This definition can also be used in multi-player games, but it is typically displaced by a much more charged meaning.
Power-leveling is most frequently employed in multi-player games, where it usually refers to a player that is of much greater power assisting a player of much lower power in defeating enemies that are far too powerful for the low-level player, but are easily and quickly killed by the more powerful player. This practice is also referred to as "tanking", where a high level character or "tank" will act similarly to the real world counterpart by acting as a shield for the low level character, thus allowing him to defeat the high level challenge without fear of penalties associated with such challenges. Defeating high level challenges rewards the lower level player with experience points more rapidly than normal. In general this is considered a form of cheating, or manipulation of the game system for unintended results. However, some view it as a stratigic means of gaining levels, especialy on single-player RPGs and among friends on MMORPGs.
Another way players may gain levels is "grinding" or constantly staying in one area of the game and killing monsters over and over. If kept up long enough it can make for very fast leveling. It is not considered cheating, but can become very tedious, and can make for there not being enough monsters left for other players to fight.
To combat power-leveling, game designers have devised better means of rewarding a player based on their actual contribution to the completion of the task. Another method used is to cap how much experience a character can gain at any single moment. For example, the game might not allow a character to gain more than 20% of the experience they need to level up by defeating an enemy. This is controversial in that it also punishes players who are skilled enough to face challenges more difficult than regular players or that band together with other players to face more difficult challenges. Another anti-power-leveling method is to base the experience given out on the highest level within the party that killed the enemy—power-levelers get around this by what could be called "passive power-leveling", where a high level character who has access to healing abilities heals the lower level character as he or she fights the enemy, or places beneficial spells on the low-level character while placing curses on the enemy.
Power-leveling increased in EverQuest as it became more common to sell characters through the Internet. Techniques of kill stealing and power-gaming would make this pursuit considerably more attractive.
Power-leveling in MMORPGs can also refer to multiple people play the same character in order to level up quicker, there are even some online services which will do this for money.
Some online companies offer power-leveling services, whereby a customer pays a fixed amount for the company to level up their character. Essentially, the customer provides the company with the username and password for their account, and the company assigns an employee to play the character for the customer until a desired level is reached.