What does voiced and unvoiced mean?

It may be referring to a music score.

A section of music that is 'unvoiced' means that part/piece is just instrumental - no voice or Words.

In another sense, it can refer to something that is inferred or assumed, but is not actually vocalized.

For example, an 'unvoiced' conclusion might 'automatically be drawn following the general united thrust of conversation about a particular issue among a particular group.