It's said that it was used by dockers in Hamburg for the first time and was later adopted by the Hamburger Hip-Hop Wave in the early 90s!
It has the same meaning as the English "mate", "dude" or "bro" depending on the context!
"Ey Digga, was geht?" - "Yo dude, what's up?"
A style of strumming the guitar to create a certain, unique sound. A Digga is a short, clean, stroke of a guitar/bass, often repeated quickly to add to the effect.
Usually played in Hardcore, Metalcore, and Post-Hardcore genres of music.
See: The Devil Wears Prada (Band)
Kirk: Yeah I know, the diggas in that song are just incredible!