A square decameter (often abbreviated as dam²) is a unit of area in the International System of Units (SI). It represents a square with sides that each measure 10 meters (1,000 centimeters) in length.
One square decameter is equal to 100 square meters (m²) because each side of the square is 10 meters long, and when you square that length, you get 100 square meters.
Square decameters are not as commonly used as some other units of area, but they can be used to describe moderate-sized land areas, and they are a part of the metric system for measuring area.
A hectare (ha) is a unit of area commonly used in many countries, especially in agriculture and land management. It is equal to 10,000 square meters (m²) or 0.01 square kilometers (km²). The term "hectare" is often used to describe the size of large land areas, such as agricultural fields, parks, and estates.
To provide some perspective, a hectare is approximately the size of a square field with sides that are 100 meters (about 328 feet) long. It's a convenient unit for measuring land area in situations where using square meters or square kilometers would result in very large or small numbers.