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.