Invasive Plant Growing in Yard?
Definitely not Japanese Knotweed, aka Fleeceflower. It may well be a Lamium. Yellow archangel (Lamium galeobdolon) is a type of lamium with variegated foliage (silver flecks on a green background) and a yellow flower. There are a couple of variegated lamium and the flower determines which one you have. All tend to be very aggressive in the landscape.