A voice vote is an unrecorded vote that is taken orally by the entire voting body rather than through a paper, electronic, or other more precise methods of tabulation.
The membership is asked to respond vocally first in favor of the question before the body by saying Aye or Yea and then separately in opposition to the question by saying nay. The chairman or presiding officer makes a judgment call as to the amount of support or opposition to the question at hand. If the response is questioned or seems inconclusive there may be alternative methods of voting employed to more precisely determine the amount of support or opposition to the question.
In order to save time, and because the members were under the impression that there was very little difference of opinion so the result would be easily identifiable, the committee chairman held a voice vote. The vote in favor of the bill was overwhelming and there was no need to poll the members individually.
US Senate Definition
"A vote in which the presiding officer states the question, then asks those in favor and against to say "Yea" or "Nay," respectively, and announces the result according to his or her judgment. The names or numbers of senators voting on each side are not recorded."