What is turbo c?

Turbo C was a type of compiling program suite for C programming by Borland for the Integrated Development Environment. It was a small and fast type of programming that was affordable and came with easy-to-use manuals.
"Turbo C" is simply the brand name used by Borland to describe the integrated development environment that supplemented their implementation of the C language. Presumably the "turbo" aspect simply implied you could produce programs quicker in their environment than in a competitor's environment. Turbo C was replaced by Turbo C++ in 1990.