What is string stream in c++?

Answer 1

Google is eager and willing

http://www.cplusplus.com/reference/sstream/stringstream/

Answer 2

A stream is an abstraction that represents a device on which input and ouput operations are performed. ... For example, file streams are C++ objects to manipulate and interact with files

Source: Ipang's link (just in case if you were not able to find the definition)