Edging is a masturbatory and porn related term. Essentially you jack-off right up until the moment you are about to cum and then you hold your penis tip hard to prevent cumming. You wait until the sensation dies down then you repeat this process, once you are finally ready to cum you will notice that your semen will shoot out of your dick and get some height as well as potency.
Pornstars do it all the time thats why you sometimes notice transitions to the final cumshot scene so you dont see the edging process.