In the 12-edo scale, the capacity for two notes with different "spellings" and musical functions to be represented by the same actual degree of the scale. For example, in the 12-edo tuning, C# and Db are enharmonically equivalent, i.e., the same note.
Below is a lattice diagram showing a "standard" Eb-to-G# 12-tone pythagorean tuning in white, its syntonic-comma equivalents (i. e., same spelling) in the lightest shade of grey, and enharmonic equivalents (i. e., different spellings represented by the same 12-edo degree) in darker shades of grey:
This usage of enharmonic equivalence also occurs in other tunings. For an example, see the final graph in the "decimal" entry.