Experience
In role-playing games, a player character's experience measures how experienced it is, often in terms of abstract "experience points" (or "XP"). Experience is stereotypically gained through combat (leading to the phenomenon of "grinding" for XP, and the tongue-in-cheek description of certain monsters as "walking XP"), though some games award XP for completing non-combat challenges successfully (or even unsuccessfully, under the reasoning that failure teaches just as much as success), and GMs are often encouraged to award good role-players with additional experience.
Depending on the system, a PC may gain levels at certain XP thresholds, and increase stats, gain access to new equipment, and learn new skills, or "spend" experience on any of those tasks.