1.A term that, in times where a physical confrontation is imminent, is used to signal ones crew, homies, gang, friends, etc. that it is time to fight.
2.To come together as a group for the purpose of fighting, rolling, or engaging in some other potentially dangerous or criminal activity
1.Guy1:"Those thugs from down the street are coming this way and they look like they want to fight" Guy2 (to the whole group):"Alright fellas Soldier Up!"
2."I think those Jones Street Boys are getting ready to pull something crazy, theres like 15 of them over there"
"Damn, they soldiered up!"