Edging is an ejaculation control technique whereby you maintain a high level of sexual arousal for an extended period of time without ejaculating. That is, you pleasure yourself right up to the edge of ejaculation and stay there, without going over.
This is often easier to practice alone, because you are the one who is aware and in control of your own stimulation and sensations, but you can also practice with a partner.
By doing so, you can enjoy direct sexual stimulation for longer and potentially overcome premature ejaculation or simply learn how to last longer. If or when you decide to ejaculate, the physical sensations are usually more intense and pleasurable.
Because edging prolongs the experience of powerful sexual sensations occurring during the final build-up to orgasm, the physical demands of maintaining this highly excited state for an extended time can induce a pleasurable, almost euphoric state.
To practice, masturbate up until the moment before ejaculation, then stop suddenly before going past this "point of no return." Notice the twitching, pulsing sensations of the impending orgasm when you stop stimulating. Or, masturbate up until the moment before ejaculation and slow down the stimulation to maintain a heightened level of sensation for an extended time, you may need to vary the speed of the rubbing or stroking of your penis to navigate right to the edge of ejaculation.
On way to think about this is with a scale of one to ten - "10" being your maximum arousal and subsequent ejaculation, "1" being practically no arousal at all. Gradually stimulate yourself to a "9" and then see if you can keep yourself there for 5min, 10min, 15min, without going to a "10" and ejaculating.
To help, masturbate to your edge then move your stimulation to another area of your body, like the lips, nipples or other erogenous zone. This can move the intense localized pleasure from your penis and disperse it through your body, heightening your full-bodied sensations and allowing further masturbation.