69 is a sexual position that allows mutual oral sex simultaneously.
To achieve this position, the two individuals normally fall down on a surface, one above the other. However, instead of being located face to face, each one placed opposite its head opposite genitalia, there by allowing that can be stimulated simultaneously.
This position is just a variation on sexual encyclopedia called Kama Sutra. There are alternatives, one of them standing on the man takes effort and takes upon himself to women who man upside will only be sustained by their legs. This position can be more motivating than the traditional 69 on the floor or in bed. Some couples practice it in front of a mirror as a stimulant.
The position taken is quite versatile, since not only can perform simultaneous oral sex: fellatio and cunnilingus (or two and two cunnilingus fellatio), but can be alternated with masturbatory techniques, which can be on the genitals or anal games too. Often it is a position that is used in the foreplay to penetration, but if the people involved provide appropriate stimulation can be very pleasurable driving to orgasm and ejaculation.
In case of male-female couples, women should always be up when this position, because if the man comes up would be very annoying, since the penis is erect and for women is very difficult to handle if it is below.
You can also get to masturbate the penis as drawing and putting it in the mouth of the woman or another man is as if the man himself was masturbating.