A yard is a unit of measurement used for qualifying volume and area, not weight. We use yards to describe volumes of soil, gravel etc., and a yard of mulch (for example) will weigh much less than a yard of gravel.

One cubic yard is defined as 3 feet x 3 feet x 3 feet.

That means that if we deliver 1 yard of top soil, that will be enough soil to spread out across an area 10 feet wide x 10 feet long, 3 inches deep.