WHAT IS RS-232C?

From Wikipedia:

"In telecommunications, RS-232 (Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). It is commonly used in computer serial ports. A similar ITU-T standard is V.24."

Or in other Words, a particular series of computer parts that allow everything in the computer communicate with each other. so it's not a particular thing, it's a type of thing. sort of like roads and railways are both ways to get places, but but use a different series of pieces and means to get to those places. RS-232 is an older way for computers to communicate and is being replaced by newer things, very slowly.