Level refers to Character Level, it forms the basis of a character's power scaling, as well as a means of gaining and improving Attribute scores. Levels are also important for unlocking features for Progressions. Character Levels are also a stat that can be used to scale Features and Metaphors.
Increasing Character Level (Level-Up)
After spending the necessary amount of Experience points, the character can increase their Level by one. Levels can only be gained incrementally, so one would have to become Level 2 before they can become Level 3 and so on. The amount of Experience points required to level up is determined by the Game-Master, usually a base number plus an increment amount (ex. 8 plus 2 for every level beyond 1st).
Level-Ups grant a few benefits: Attribute Point(s), Attribute Training Opportunities, and unlocking more of a character's Progressions.
Attribute Point(s)
After a Level-Up, characters can assign an amount of Attribute Point(s) to any of their six Attributes, which in turn can improve their Core Values. Characters get +1 Attribute points if they have one or more Progressions, else they would get +2 per level instead.
Whichever Attribute the player wishes to assign to a character, they can't choose an Attribute if its value would exceed their character's level. Also, if the character gets two or more Attribute points per level, they can only improve an Attribute by one point each per level.
Attribute Training Opportunity (ATO)
ATOs are the number of times a character can increase an Attribute score by one by spending an appropriate amount of experience points. Usually the XP cost is equal to the current Attribute + 1, and the opportunities given is double the character's level.
The player can't improve an Attribute to be higher than the character's level, nor can they improve the character's Attribute more times than they have opportunities.