Pass is a call whose natural meaning is unwillingness to make any other calls. Normally, you passes when
- you have nothing more to say, and
- your partner has not made a forcing bid.
The only correct form, when spoken, is the single word pass. When bidding on a bidding sheet, the correct form is a '/'. Abbreviations used in literatures include P, - and /.
A natural pass is always non-forcing.
Pass is (usually) a limit bid.