(a) "Yard" means an open space at grade between a building and the adjoining lot lines unoccupied and unobstructed by any portion of a structure from the ground upward, except as otherwise provided herein. In measuring a yard for the purpose of determining the width of a side yard, the depth of a front yard or the depth of a rear yard, the minimum horizontal distance between the lot line and the main building shall be used.
(b) "Front yard" means a yard extending across the front of a lot between the side lot lines and being the minimum horizontal distance between the street right-of-way and the main building or any projection thereof, other than the projections of the usual uncovered steps, uncovered balconies or uncovered porch.
(c) "Rear yard" means a yard extending across the rear of a lot and being the required minimum horizontal distance between the rear lot line and the rear of the main building or any projection thereof, other than the projections of uncovered steps or unenclosed porches.
(d) "Side yard" means a yard between the main building and the side line of the lot and extending from the required front yard to the required rear yard, and being the minimum horizontal distance between a side lot and the side of the main building or any projections thereto.