What does it mean to say that C was compiled in C? [duplicate]

Question

I've seen stuff like this written... C was written in C, or ABAP was written in ABAP..

I've even seen one guy saying that this is one of the criteria to sort languages into true programming languages.

I'd like someone to explain to me what this means.

Thanks in advance.

EDIT:Changed title from: "C was made using C" to "C was compiled using C".

Answer 1

You start with assembly, you make a first version and can always write a new version of a compiler with the previous version.

You do not need a compiler in order to start compiler written in its language. You just need to write an interpreter for a C subset. Then you use this subset in order to enhance it.

At the time C was invented (around 1967) nobody thought it was a sane idea to write a compiler or an Operating System in a high level language, except Brian Kerninghan and Dennis Ritchie. They proved to be right!