When two people are docking (see docking), and others want to get involved, the other parties take part by inserting their penis into the anus of one of the parties docking. (Socket Docking)
Tom and Luke were docking and Ryan and Jesse got held they were left out. They positioned themselves behind Tim and Luke to take part. Socket Docking.
When you’re having a threesome with a girl and your boy, you take the back end and your boy takes the front end. You are both distance docking. Park that boat.
Pocket docking is the act similar to docking in a sexual context.
The “Pocket” variation is when one of the persons involved in the docking has transitioned from male to female. As they once had a penis and now have a vagina, creating a “pocket” (crude term for vagina).