Circle is the primary measure of guild advancement. It is the accepted in-character term for what is essentially identical to "level" in other RPG's. A novice begins at first circle, and when sufficient experience has been acquired, may then progress to second circle, and so on.
Circles are granted by Guild Leaders based on an adventurer having achieved a set of defined minimum ranks in a variety of skills, as appropriate for each guild. Given DragonRealms' emphasis on skills, circle is not always an accurate shorthand for a given character's ability or power, as nothing prevents a character from training skills not required to circle, or in excess of circle requirements.
Many guild abilities and spells require achieving a certain circle before they are granted. Circling also provides a bonus amount of TDP's, which can be spent to train stats or access additional benefits.