The double type stores numbers with decimal points, like 3.14, -0.5, or 2.0. It uses 8 bytes and can represent large or small numbers with about 15-17 digits of precision. Unlike int, double can store fractional values.
When you divide 7.0 / 2.0, you get 3.5, not 3. Example: double pi = 3.14159265359; stores pi with high precision. You can then use it in calculations like 2 * pi * radius.