A dictionary of common swingers' terms:

Literally, Big Beautiful Woman, and is used to refer to women who are overweight or obese but who are comfortable in their bodies and feel sexually attractive - and are sexually attrative to many people.
Bi-selfish usually refers to women rather than men who are happy to receive oral sex from someone of the same gender but would not want to give oral sex in return.
The practice of having unsafe sex without a condom. Originally this was a slang term in the gay community for unprotected anal sex but it is now in general use.
420 Friendly
Four-twenty is a common American term for being comfortable with using cannabis. The term originally came from a group of teenagers at San Rafael High School, California who used to meet up at 4.20pm to smoke cannabis.
Off-premises Club
Swingers club where sex is not allowed in the club. The club will typically have a bar and a dance floor and will be for socialising and meeting new people.
On-premises Club
Swingers club where sex is allowed in the club as opposed to an off-premises club which is just for meeting swingers but any sex would happen elsewhere.
Soft Swing
Soft Swinging does not involve penetrative sex with another partner. Typically it will include touching, oral sex or two couples having full sex with their own partners in the same room.
Height and Weight Proportionate, in other words not overweight.
Sex outside while watched (or joined by) others. There are two explanations for the term, one is that it the excuse if caught would be "I was just walking the dog" and the other is that it refers to single men who would "dog" the couple trying to have sex.
AC/DC is a slight out of date term for bisexual. It comes from the eletrical term where AC/DC equipment can take either type of electricity (alternating current or direct current).
Mother I'd Like To Fuck. The expression was made famous in the movie American Pie, "Dude that chick's a MILF!".
Very well endowed. Refers to a gentleman's penis, usually one over 7" in length. VVWE revers to a Very Very Well Endowed gentleman. More V's equals more length. As in "Only VVWE guys need apply".