To pass trough a non-smoking area with a lit cigarette. What makes a walk-through different from just smoking
in the house (or wherever) is that
the person makes an effort to get to the next smoking area as quickly as possible. In addition, hitting the cigarette nullifies the walk-through and thus constitutes "smoking
in the house."
Rob: Hey I'm going out back, is it ok if I walk-through?
Marty: Yeah, go for it.
{As Rob is executing his walk-through from
the front porch to the backyard he encounters Morgan}
Morgan: Hi Rob! How's is going?
Rob (with
cigarette raised): Not bad, but
I can't talk. I'm doin a walk-trough.