Street fighting is hand-to-hand combat in public places, between individuals or groups of people. Unlike sport fighting, a street fight might involve weapons, multiple opponents, and no rules. The venue is usually a public place (e.g. a street) and the fight sometimes results in serious injury or occasionally even death. Some street fights can be gang-related.
The main difference between street fighting and a self defense situation is that a street fight is avoidable, whereas a self-defense situation is not. The other main difference is that the fight is consensual between both parties. A typical situation might involve two men arguing in a bar, then one suggests stepping outside, where the fight commences. Thus, it is often possible to avoid the fight by backing off, while in self-defense, a person is actively trying to escape the situation, using force if necessary to ensure their own safety.
In some martial arts communities, street fighting and self-defense are often considered synonymous.