Premature ejaculation means ejaculation takes place before the man inserts his penis into the vagina, or one to two minutes afterwards or there is an inability to delay ejaculation in all, or almost all, episodes of penetrative sex. Sometimes totally unable to achieve ejaculation.
Ejaculation is where semen is squirted out of the penis during an orgasm (sexual climax). Early ejaculation is quite common, with an estimated 20-30% of men experiencing at least one episode during their lifetime.