Decan
A decan divides each 30° sign into three 10° sections. It is a zodiacal subdivision, not an additional sign.
How it is defined
The first section runs from 0° to under 10°, the second from 10° to under 20°, and the third from 20° to under 30°. Rulers vary by tradition.
How to read it
Symbols work in combination: a sign modifies a function and belongs to an element and modality. That combination provides more context than an isolated label.
A concrete example
A position at 12° of a sign belongs to its second decan. Assigning a ruler also requires specifying the table or school used.
Explore further
Compare Sun, Moon and ascendant within one chart. Identify which factor you are reading before applying a general description to your own situation.