Abbreviation (and "pet name"!) for K&R, second edition (as in Brian Kernighan and Dennis Ritchie's The C Programming Language, second edition).
This is the edition you want to read (unlike the first edition, which is the one you want to own; no offers will be considered, so go bug someone else!). It describes ANSI C, rather than the older language (sometimes named "Classic C" and always remembered with a fondness that inexplicably ignores the horrors of actually programming in it).