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 at any time.

It's worth noting, that for combat-earned Experience, killing or destroying enemy is merely default and most obvious method. Other methods include: forcibly removing the opponent from the battlefield; knocking the opponent out; incapacitating the opponent by putting him in a state in which he can not harm you; exact amount of time the opponent must be inoperable to count victory varies depending on GM (1 week, 1 hour and 1 day respectively are upper limit - most GM's count victory way earlier). Forcibly turning enemy into ally under your control also counts, as does making enemy surrender. Making enemy route or sneaking past enemy without being detected may also count as victory, depending on circumstances. Experience can also be given, if mission objective was completed, even if all enemies weren't defeated (e.g. get MacGuffin and return to base; enemies had job of protecting/getting MacGuffin, which they failed, therefore they "lost" - cue EXP reward) - though, EXP for completed mission and EXP for defeated enemies may be same thing or separate. In some game systems, merely detecting enemy and surviving the encounter with it gives Experience, though less than for defeating that enemy.