Voice refers to the relationship between the subject and the main verb. There are two voices in the English language: active and passive. Test writers tend to have a stylistic preference for the active voice over the passive.
Verbs in the active voice place the performer of the action in the subject role and the person or thing that receives the action in the object position.
Most sentences contain verbs in the active voice:
Andy throws the baton.
The octogenarian plays the harp.
In both cases, the subject is doing the action indicated by the verb. The object is “receiving” the action indicated by the verb.
The situation is reversed in the passive voice. In a passive construction, the former object becomes the subject, and the performer either occurs in a prepositional phrase beginning with “by” or is omitted from the sentence altogether:
The baton was thrown (by Andy).
The harp was played (by the octogenarian).
As a general rule, the passive voice is both less forceful and less clear than the active voice.
In general, passive voice (alone) isn’t sufficient to make a GMAT question wrong.