What is meant by 'flushing the stream'?

Question

I\'ve read that \'\\n\' is preferred over \'endl\' for new line in c++ because \'endl\' inserts new line and flushes the stream. Please tell me what is flushing the stream ?

Answer 1

Flushing a stream ensures that all data that has been written to that stream is output, including clearing any that may have been buffered.

Some streams are buffered to aid performance, e.g. a stream writing to disk may buffer until the content reaches a block size.