In games derived from Dungeons & Dragons (D&D), an accumulation of a sufficient number of experience points (XP) increases a character's "level", a number that represents a character's overall skill and experience. To "level" or "level up" means to gain enough XP to reach the next level. By gaining a level, a character's abilities or stats will increase, making the character stronger and able to accomplish more difficult tasks, including safely battling stronger enemies, gaining access to more powerful abilities (such as spells or combat techniques), and to make, fix or disable more complex mechanical devices, or resolve increasingly difficult social challenges.
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.
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.
Some games have a level cap, or a limit of levels available. For example, in the online game RuneScape, no player can currently get higher than level 120 which needs a combined 104,273,167 experience points to gain, nor can any one skill gain more than 200 million experience. Some games have a dynamic level cap, where the level cap is dependent upon the levels of the average player (so it gradually increases).
In some systems, such as the classic tabletop role-playing games Traveller, Call of Cthulhu and Basic Role-Playing, and the role-playing video games Final Fantasy II, The Elder Scrolls, and the SaGa and Grandia series progression is based on increasing individual statistics (skills, rank and other features) of the character, and is not driven by the acquisition of (general) experience points. The skills and attributes are made to grow through exercised use. Some authors believe that activity-based progression encourages tedious grinding processes, like intentionally taking damage and attacking allied characters to increase health in Final Fantasy II, or forcing player to jump constantly to increase acrobatics skill in The Elder Scrolls series.
Free-form advancement is used by many role-playing systems including GURPS, Hero System or the World of Darkness series. It allows the player to select which skills to advance by allocating "points". Each character attribute is assigned a price to improve, so for example it might cost a character 2 points to raise an archery skill one notch, 10 points to raise overall dexterity by one, or it might cost 20 points to learn a new magic spell.
Players are typically free to spend points however they choose, which greatly increases the control that a player has over the character's development, but also usually causes players to find that complexity increases as well. Some games therefore simplify character creation and advancement by suggesting packages or templates of pre-selected ability sets, so for example a player could have their character become an "investigator" by purchasing a package deal which includes many skills and abilities, rather than buying them each separately.
A cash-in experience advancement system uses experience points to "purchase" such character advancements as class levels, skill points, new skills, feats or increasing saving throw bonuses or base attribute points each of which has a set cost in experience points with set limits on the maximum bonuses that can be purchased at a given time usually once per game session. Once experience points are used thus they are "spent" and are erased from the character record or marked as spent and cannot be used again. Final Fantasy XIII and Warhammer Fantasy Roleplay are examples of games that use a cash-in advancement system.
Some games use advancement systems which combine elements from two or more of the above types. For example, in the third edition of Dungeons & Dragons, whenever a level is gained in a character class, it provides a number of skill points (the exact number is calculated based on the class and the character's intelligence statistic), which can be spent to raise various skills. Character level (generally the sum of a character's total levels in all classes) is used to calculate how high skills can be raised, when an ability score can be raised and when a character can gain new feats (a class of special abilities which include special attacks, proficiencies in various weapons and bonuses on the dice rolls used to determine the outcome of various actions) and how many experience points are needed to advance in level. In Ragnarok Online, experience points are divided into two categories: base experience and job experience. Gaining base experience increases a character's base level, which is used to calculate a character's maximum HP and SP, increasing base level also provides points which can be spent to increase stats such as strength, agility and intelligence. Gaining job experience increases a character's job level, each job level provides a skill point which can be spent in the job's skill tree to gain a new ability, such as a spell, special attack or passive bonus, or improve an existing ability.