The slash is often used, perhaps incorrectly, to separate the letters in a two-letter initialism such as R/C (short for radio control) or w/o (without). Purists strongly discourage this newer use of the symbol. However, since other uses of the slash with individual characters are highly context-specific, confusion is not likely to arise. Other examples include b/w (between or, sometimes, black and white), w/e (whatever, also weekend or week ending), i/o (input-output), and r/w (read-write).
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http://goo.gl/0JO1