A Rank (ランク, Ranku) is an indicator that is exclusive to Xyz Monsters, used in place of a Level. It is indicated by a number of stars, similar to a Level; however, they are aligned at the left side of the card, and are depicted by a yellow star on a black circle. The Rank of an Xyz Monster is the same as the Level of its Xyz Materials.
An Xyz Monster's Rank is not its Level. Xyz Monsters do not have a Level. Therefore, they cannot be used for Synchro, Ritual, or Xyz Summons (except for Rank-Up and Rank-Down), and any effects that would refer to the Level of a monster, such as those of "Gravity Bind", "Level Limit - Area B" and "Burden of the Mighty", cannot be applied to an Xyz Monster.
Since Xyz Monsters do not have Levels, cards such as "Star Changer", "Scanner" and "Give and Take" cannot be used on them at all. Cards that modify Levels such as "Harmonic Waves", "Feedback Warrior", "Synchro Boost" and "Demotion" also cannot be used on Xyz Monsters. If the only monster on the field is an Xyz Monster, those cards cannot be activated.
The ATK averages for Ranks are a fair bit higher than for their respective Levels (for example, Rank 3 monsters without negative effects can reach 2100 ATK and Rank 4 monsters can reach 2600 ATK, compared to 1750 ATK for a Level 3 monster and 2000 ATK for a Level 4 monster). Just like any other category of monsters, Xyz Monsters with more powerful effects may have lower ATK and DEF than other monsters of the same Rank.