This is the normal algabraic symbol used in textbooks and derivations for the item in question.
It should be an un-ambiguous symbol as used by the discipline in question, hoever, as there are only limited versions of Greek and Roman letters this will mean that the use of x, y, θ, ρ, and φ will be rather common and that persons who are not close to the original work will have to be very careful about assuming that the symbol is used the way they would use it – and may have to rely on the key code itself to understand the actual definition.