Sparteye, what is a walk-out?

A walk-out is a house constructed on a slope, so that at least one side of the bottom floor is at ground level. The walk-out level has the construction attibutes of a foundation floor, but is (usually) finished and is used as living space. So-called because one can walk out of the house from that floor through a door directly to the outside.

Example: my house appears to be a two-story house when viewed from the front, with the first floor (called ground floor, I think, in the UK) at ground level, having the main entrance to the house and the general public living areas of living room, dining room, kitchen and so on. But, when viewed from the back, due to the slope of the ground, the house has another, lower floor. From the back, entrance to the backyard is from the level below the first floor. That lower level/basement has a finished recreation room, a bar and a bathroom, and doors and windows to the outside. To access the first floor from the backyard, you must go up steps to a deck and then to doors which go into the sunroom or garage.