Arguably (
AFAIK) the most popular
scale, or
gauge, of
track in
model railroads. Any
model train you buy in KB Toys is probably HO scale. I don't know exactly, but the HO track is about 1.5 inches wide and each car is from 6-10 inches long.
Addendum/Correction: HO gauge, according to the Lionel web site, is 5/8" wide, making the trains 1:87 scale. I guess my memory is from holding them with smaller hands. Damned perception!