# What is the fundamental difference between ghost and auxiliary fields?

I am somehow confused by the notion of auxiliary fields, such as for example the fields $F$ and $D$ which appear in supersymmetry, and the notion of ghost fields which appear for example in the BRST formalism. Both kinds of fields are deemed to be not physical.

Can somebody once and for all in a clear cut way explain to me what the fundamental differences (and similarities) between ghost and auxiliary fields are?