Bondage mags (or bondage magazines) are hardcore porn magazines aimed at people who have an interest in bondage or BDSM. BDSM stands for bondage and discipline and sadism and masochism. Bondage is a favourite of men and women who like to feel a sense of dominance and empowerment during sex. Bondage includes tying people up so that they are totally submissive, and also includes ideas of pain mixed with pleasure, in the S&M side of bondage.
Some people regard bondage and S&M as weird, and maybe even sick, but these are people who haven't tried it and haven't opened their mind to sex games and real sexual foreplay. Many people don't involve themselves in enough sexual foreplay, and if bondage is used in a comfortable way to both consenting parties then it can be a great arousal and a very sensual form of foreplay.
The idea of bondage as foreplay is the part that appeals to women. Women differ sexually to men in that it takes longer to warm a woman up and get her going than it does for a man. Usually the man is up and away and gets down to the fun, and by the time he's finished the woman is just ready to go, leaving her lying horny and unsatisfied, but he's finished and probably off to sleep for the night. With some good long sexual foreplay like bondage the woman gets fully turned on before sex begins and so when the intercourse begins both the man and the woman are on an equal start and ready for some good mutually orgasmic sex.
The bondage culture originates in the post World War 2 leather biker culture, where disciplined and regimented WW2 veterans who wore old guard leather in the war brought there military traditions into their home life and sex life. The leather bondage culture began as a homosexual one, but spread out throughout all sexual orientations as the thought of bondage became sexually arousing to men of all orientations, as well as women.
Bondage mags made an emergence in the 1950s, but with a crack down in porn in this era bondage mags disappeared for a couple of decades, and made a re-emergence in the 70s. In the late 70s bondage started to be more accepted by heterosexual couples, and bondage mags became more popular, and to meet the demand more names in the bondage mags scene made an emergence.
In the world of the internet and its dominance over porn, bondage mags have seen a bit of a slump with many of the old names dying off. This hasn't meant the death of bondage mags though - there are still quite a few bondage magazine suppliers out there, but unless you know where to get them they can be hard to find - the best place to look is on hardcore magazines.