Sheepshead/walk

In Sheepshead, the term "walk" refers specifically to non-trump suits (and most often the the called ace suit[?]). If it walks, that means that no trump was played and the Ace won the trick.

Note about Called Ace:

Since neither picker nor partner can play trump on the called ace suit, it leaves the opponents an opening to easily trump the trick. For this reason, the picker/partner normally do not want to lead the called suit too early in the hand. It's better for the picker to lead trump and try to bleed the opponent's trump supply before leading the called suit. Conversely, the opponents generally want to lead with the called suit as early in the hand as possible.

See also : Sheepshead