I use the term myself to mean that the pairing feels very right and special and means a lot to me, and I'm not interested in casually breaking the guys up and putting them with someone else. But I have wondered what it means to other people, because it seems that the term OTP is used a great deal by wackos who send nasty e-mail to anyone who dares to write one of "their characters" sleeping with a character they don't approve of, or who will persecute people for not writing the OTP pair "correctly." So I'm not sure what it means in fandom overall. For me it just means "special pairing that I really love." Somebody else can write one of the guys with somebody else and it's OK with me.