Answer 1

A namespace is a declarative region that provides a scope to the identifiers (the names of types, functions, variables, etc) inside it.
And
iostream stands for standard input-output stream. This header file contains definitions to objects like cin, cout, cerr etc.
For more info visit this link,
https://www.google.com/amp/s/www.geeksforgeeks.org/basic-input-output-c/amp/
and also check this question,
https://www.sololearn.com/discuss/1274254/?ref=app
https://www.sololearn.com/discuss/1579583/?ref=app