Simplify the following text for a Grade 5 native English-speaking person.
Original: In 1795 , when the metric system was introduced , the are was defined as being 100 square metres and the hectare ( ` hecto - ' + ` are ' ) was thus 100 ares or 1\/100 km2 .
Simplified: A square plot of land with 100 m length for a side , is one hectare .