English writing often uses slashes to form two-letter abbreviations, plus the one-letter w/ – some examples, roughly in order of frequency: I/O – “input/output” w/ – “with” c/o – “care of” A/C – “air conditioning” w/o – “without” R/C – “remote control” b/c – “because” Like most abbreviations, these are less common in formal writing, although some of.