It's a buzz a cocksucker gets after swallowing a load of cum, esp. a big load or several in a row. Attributed to the testosterone level in the cum, varies per load and/or dude getting blown. Some cocksuckers become addicted to the feeling.
A: I had a cum rush all night long from that load you shot down my throat last night.
B: Told you it was worth it.
A: When you want to get together again?
B: This is just between us, cool?
when you are fucking a girl and you look up at the clock and start pounding hard as to quickly cum because your late for class/work
sean- hey man where u been? you fucking late man!
chris- yeah sorry i was at kristinas, i had to cum rush
sean- oh cool was she any good?
chris- shut up sean u fucking retard!