Go deep relates to a number of things, mainly sexually orientated. It may be used in the following sexual contexts:
Using a raised voice - GO DEEEP! - when the vagina is propped up and ready for insertion. This catch phrase is often helpful for increasing focus for the task at hand. The penis is inserted
at a medium pace, ensuring full length penetration. The first stroke often sets the mood for the remainder of the session, so it is cruicial to maintain direction and speed, and ensure maximum depth into the vaginal cavity.
Alternatively, the partner (or receiver) may request the giver to 'go deep', which following guidelines of the first context, also sets a great mood.
In a baby making context. To
go deep is to ensure the ejaculate from the male testes is deposited as close to the uterus as possible. This ensures the semen has the least distance to travel through the cervix, as the
spermicide contained within the vaginal walls battles with the foreign invaders (similar to the
asian invasion occuring in Australia... you know who you are!).