Check

The "Check" command can be found in the menu that pops up when you select a target, or by using /check or CTRL+C. It allows you to view the level and equipment on other players, and gauge the strength of enemies.

Checking Players
Usage of this command on another player will allow one to view that player's Equipment and Bazaar. Also, if that player is not /anon one will see current Job level, Subjob level, and Title.

Checking Enemies
Usage of this command on enemies will allow one to ascertain a rough idea of the enemy's relative strength via the following messages:

Too Weak to be Worthwhile Abbreviation: TW
 * A Too Weak to be Worthwhile enemy is 7+ levels below you at level 1, or 20+ levels below you at level 75.
 * These enemies do not aggro unless you rest, and give no experience points when killed.

Easy Prey Abbreviation: EP
 * An Easy Prey enemy is 3-6 levels below you at level 1, or 8-19 levels below you at level 75.
 * Enemies on the low end of EP (13-19 levels below you at level 75) do not aggro unless you rest.

Decent Challenge Abbreviation: DC
 * A Decent Challenge enemy is 1-2 levels below you at level 1, or 1-7 levels below you at level 75.

Even Match Abbreviation: EM
 * An Even Match enemy is the same level you are.
 * A solo kill of an Even Match monster gives 100 experience points before modifiers.

Tough Abbreviation: T
 * A Tough enemy is 1-4 levels above you at level 1, or 1-3 levels above you at level 75.

Very Tough Abbreviation: VT
 * A Very Tough enemy is 5 levels above you at level 1, or 4-7 levels above you at level 75.

Incredibly Tough Abbreviation: IT
 * An Incredibly Tough enemy is 6+ levels above you at level 1, or 8+ levels above you at level 75.
 * "IT+" means the monster checks as Incredibly Tough, High Defense.
 * "IT++" means the monster checks as Incredibly Tough, High Evasion, High Defense.

Impossible to Gauge
 * An Impossible to Gauge enemy is a notorious monster and no further information can be given.

In addition to the relative level, checking a monster will tell you about their defense and evasion.

High Defense
 * If a monster checks as high defense, your hits will usually do less than the damage rating of your weapon.
 * A monster checks as high defense if your Attack is lower than its Defense.

Low Defense
 * If a monster checks as low defense, your hits will usually do more than the damage rating of your weapon.
 * A monster checks as low defense if your Attack is at least 25% higher than its Defense.

High Evasion
 * If a monster checks as high evasion, you have a lower than __ (50% maybe?) chance to hit it.
 * Mathematically, your accuracy < Enemy evasion - 30

Low Evasion
 * If a monster checks as low evasion, you have a greater than 75% chance to hit it.
 * Mathematically, your accuracy >= Enemy Evasion + 10