c++11 - What's the meaning of [=](...){...} in C++?

What is the effect of this statement:

std::replace_if(ln.begin(),ln.end(),[=](int c){return c=='\n'||c==' ';},0);

Specifically, I'd like to know:

What's the meaning of

[=](int c){return c=='\n'||c==' ';}

Where's the grammar for this defined?