It means to get yourself very, very close to orgasm, where just a few extra hard rubs or vibes would take you over, and to keep yourself there for as long as you can.
Some find it harder than others. Some find they can ‘bounce’ to that edge but it drops off fast and they have to rub harder again to get there.
If you can find it though, and learn to manage to hold it, it’s something else. It’s quite the ecstatic experience, almost out of body – in fact lots of the tantric sex thing is based on the idea. Some say it’s even better than an orgasm as you can learn to stay there for much longer.
The real key to staying there, is keeping relaxed. Get your breathing steady and slow and keep it that way, it’s a balance between all that pleasure going into you and letting it out so it doesn’t overwhelm you and you cum.
Try it, and be nice to yourself, It takes practise, so don’t feel bad about slipping over into orgasm. Women tend to stay on that ‘orgasmic plateau’ even if they cum or ruin it, so don’t think that because you ‘failed’ you have to stop, get back to the edge, and try again, and again, until you start to be able to stay in that place and become a true ‘edge rider’.