What is the significance of term "using namespace std"?

[idontknowhowtocode (Rohit Singh)]

I have seen in many codes people avoice using writing “using namespace std” and just cast "std:: " or something like that, why ?
the code can be simplicated by putting “using namespace std” on the top then why some people prefer not to use that ?

[phantom (sharad nailwal)]

hi rohit
it does not have a proper and does not affect code ans both of them are right
as earlier std was used
so it might be a habit or something else.
but yes using namespace will definetly help the code to look more good