Leeching refers to the practice of joining a "MapleStory" party and then collecting experience points while not doing any actual work for the points. Every time someone in your party kills monsters, it counts as experience for the whole party, and everyone will get points. If you are a member of the party and simply let your character stand there, not helping with the quests or in-game work such as killing enemies, you are leeching.
Most Effective Leeching
To engage in leeching, you will have to first choose a party to join. The most effective leeching can generally be accomplished by joining a party with high-level players who can inflict a great deal of damage. For example, Bishops and Arch Mages can kill as many as 15 monsters at one time, making battles relatively fast and easy. Playing in a party with level 200 players (the highest possible level) is an effective way to gain experience fast.
Leeching Experience and Monster Levels
In order to gain experience from a monster kill, you must be at a level within five levels, or higher, than the level of the monster killed. For example, if a level 95 monster is killed by anyone in your party, you will receive a share of the experience points only if you are at level 90 or higher yourself.
Experience Amounts Gained
The amount of experience you gain from leeching will depend upon your level. Higher level players will receive higher amounts of experience points, and the least experience points will be given to the lowest level players. This helps prevent level jumping: If the experience points you receive as a low-level player from a monster kill were the same as the high-level players receive, it would cause you to "jump" multiple levels at once, which can't be done in "MapleStory." For example, a level-three player who receives experience can only advance to level four and cannot receive massive experience that would cause a sudden jump to level six.
Leeching can be a costly way to level up. High level players can charge millions of mesos for the privilege of joining their party, so you will regularly need to purchase a place in such parties. Buying into such a party can be a risk because some scammers have been known to offer places in their party, take money from unsuspecting players, and then not actually allow them into the party. Leeching may also work against you in terms of knowing how gameplay really works: If you leech your way to high levels, rarely participating in actual gameplay, you will know very little about how to actually play "MapleStory" and how to advance your character in the standard way. Leeching is also frowned upon by many regular "MapleStory" players -- it is often regarded as a game cheat that can allow novice players to simply "buy" their way through the game.