What is double?

Answer 1

More memory is allocated for double precision.

Double accommodates 15 to 16 binary digits (Depending on whether signed).

So double can range from approximately 5.0 × 10−345 to 1.7 × 10308.

Here are some existing threads for your reference.
https://www.sololearn.com/discuss/660920/?ref=app
https://www.sololearn.com/discuss/2064589/?ref=app
https://www.sololearn.com/discuss/736163/?ref=app

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Answer 2

The double data type is a double-precision 64-bit IEEE 754 floating point. in other word it is long form of point no.