What does the abbreviation ha mean?

The abbreviation 'ha' stands for hectare, which is a unit of square measurement like an acre.

One hectare is about the size of a football/soccer pitch, or about 2.5 acres.

Hectare is part of the SI (International System) of units, the modern metric system. Most countries in the world now use SI instead of the traditional measurements. USA and UK are the main countries that still use the old units (UK policy is to change, but the change is still happening). 10 000 m2 = 1 ha

100 ha = 1 square km (kilometer)