Why do we need "alphabets" defined?

Question

I'm reading over my computational theory book before quarter starts and it's giving me the following definitions.

alphabet: any nonempty finite set

symbols: members of the alphabet

I don't understand the relevance of why this term even needs to be defined. It seems unnecessary. What exactly differentiates this from any regular set that has a cardinality greater than 0?

Answer 1

Answered in the comments by Brian M. Scott:

Nothing but the context in which the term is used. The terminology turns out to be useful, and it’s the terminology that’s being defined here, not the concepts.