What does the syntax f.(10) mean?

In irb I have defined the lambda

f=lambda { |x| x+1 }

and then issued (because I have seen it in someone else code)

f.(10)

which computed 11. But what does the f.(10) syntax mean? It computes the
same as f(10), but why?

f.(10) is an alias for f.call(10) - see documentation for Proc#call
http://ruby-doc.org/core-2.1.4/Proc.html#method-i-call

f(10) won’t work, you’ve probably meant f[10] as an equivalent method
call.

Thank you!