C++ is a programming language created by Bjarne Stroustrup and first released in 1985 as an extension to the C language. It was originally C with the addition of classes, but has expanded significantly to include full object-orientation and a host of other features such as low-level memory management. The language continues to see updates and major releases are put out ever couple years. It is one of the most widely-used programming languages in the world, and most professional programs made for Windows are written in C++. The name "C++" is used because, in C, the operator ++ adds one to a variable. For this reason, there is no "C+".
I know only the most basic aspects of C++. I find the language to be needlessly complex and too abstract and symbolic to be enjoyable to write in. A large part of this comes from the fact it is derived from C, of which, I have the same criticisms, but at least C is much simpler to learn. For C-like languages, I prefer C#.