It means what it says: the vocal part was "double-tracked," i.e., recorded twice. Two separate passes were recorded and both vocals saved on the master tape. They were mixed split in this case, which made the effect a little easier to spot. Sometimes it isn't clear whether there are actually two different vocal performances, or just one, with a little delay or echo added to "fatten up the vocal."

On "Never Comes the Day" (especially during "if only you knew what's inside of me now...."), you can hear Justin's voice separately in the left and right ears. The melody was sung separately for each side. There are very slight differences, such as accenting a given word a little more on one side or holding a note slightly longer on one side over the other. Tony Clarke, producer of the first eight albums with Justin Hayward and John Lodge, often used this effect.

Using headphones/headsets makes this easier to hear. Some songs that are recommended to listening with headphones (for this and other effects) are: "Legend of a Mind," "Never Comes the Day," "The Best Way to Travel," "The Story in Your Eyes," "Floating" and, one of the best examples of all, "Nights Winters Years" from the Blue Jays album.