What is it?
Objective C is a high level programming language that borrows a lot from C - adding features such as object-oriented design patterns and garbage collection.
It is used primarily in developing software for Apple products and XCode is its IDE of choice.
What is it like?
Powerful and fast, but it has a steep learning curve and the syntax is quite verbose when compared to other similar languages.
With that said, it is very well documented and has a large community but Apple are encouraging users to move to the more modern Swift programming language.