A no-disqualification, no-countout match where anything goes. But falls still have to happen in the ring, if they count anywhere, that is a separate Falls Count Anywhere stipulation. Wrestlers usually come out in street clothes instead of gear to sell the 'this is personal, not a wrestling match' vibe. The street fight is the catch-all stipulation for feuds that have gotten too heated for a normal match. It's also an excuse to use every weapon under the ring.
"They're brawling through the crowd, up the stairs, into the concourse. Someone just got thrown into a merchandise table. This is a street fight."