The hectare (abbreviated ha) is a unit of area equal to 10,000 square meters and used exclusively for measuring land. To get a sense of how big this is, imagine a football field. A football field is almost exactly 100 meters from one end line to the opposite goal line.
Imagine a square of that length on each side, and you’ve got an area of one hectare. There are 100 hectares in one square kilometer, so one square kilometer is the same area as a square that is ten football fields on one side.