In a sexual context, the phrase 'to completion' describes engaging in a sexual act to the point of orgasm. It is most commonly used to describe fellatio that ends in ejaculation. It can also be applied to penetrative sex or masturbation which concludes in orgasm.
The phrase comes from the more common sense of the word completion, meaning to see a project through until it's finished.
More About To Completion
For many couples, taking any sex act to completion helps them enjoy mutual pleasure and strengthen their bonds. An orgasm feels powerfully pleasurable, and most people also take joy from giving this pleasure to an intimate partner.
However, for people of some religions, taking a sex act like fellatio to completion is considered a sin. For example, people of the Catholic faith believe that spilling semen outside the womb is immoral because it diminishes the reproductive purpose of sexual interactions.
The phrase to completion can apply to sex acts enjoyed between couples and solo exploration. Masturbating to completion involves sexual stimulation, typically with the hands or a sex toy, to the point of orgasm.
Many people consider having penetrative sex to completion as having sex until a male ejaculates. However, others believe that sex to completion should involve the orgasm of both partners. This definition also does not consider what to completion might mean to couples that are not straight, such as a lesbian couple.