One Hectare equals to one square hectometer or one hundred ares. This in square meters results in 10,000 m². To get the idea of what represents one hectare, just imagine a square terrain, with one hundred meters on each side. If you are a football fan, you can use the measure of the area of the playing field as equivalent to about one hectare. This is essentially an agrarian measure, widely used in calculating the size of agricultural areas, forests and natural areas. For example, at the time of fires, the burning area is always expressed in hectares.
Acre is an old unit of measurement used to measure land. The term comes from Old English which means "field drawn". During the Middle Ages, one acre represented the amount of land that could be plowed in one day with a cow. This is a unit of measure with little used currently. It can still be found in literature, being its most famous reference, The "Hundred Acre Wood", that is a fictional forest where Winnie-the-Pooh and its friends live.