Street Defence, Self Defence, Self Protection. All martial arts have self defence applications.  Where arts tend to differ is in their approaches to training and the application of the techniques.

Street Defence is not a sport or specific martial art but a collection of practical techniques to protect you in your every day life.  There will be an emphasis on avoidance, reading potential situations and simply not being there to be involved.  Why walk across a scrub piece of land late at night if you think you might be attacked.  A shortcut ? Take the long way around and be safe !

Techniques – no jumping spinning kicks here – low effective kicks and more often as not open hand strikes.  Hitting first and hitting hard and using subterfuge on your attacker before they get chance to use it on you.
Weapons – you may be attacked or threatened with and edged weapon, dagger or craft knife, or blunt objects such as baseball bats, hammers pool cues even chairs etc..  You may be able to use improvised weapons yourself.  There are even defences against guns in certain circumstances.

All these techniques are used as a last resort.  Emphasis on last resort !!

Krav Maga has a structured syllabus and network of clubs and instructors around the world;  But there are many noteworthy self defence styles, clubs and instructors to choose from. i.e. Geoff Thompson's - Real Combat System  or CQC (close quarter combat) (example site)..
Most traditional martial arts clubs also have a high content of practical techniques such as Ju Jitsu where as sport martial arts, such as kickboxing and Judo may not use the most obvious technique as it may be illegal in competition.   i.e. Judo will start from some sort of grip and striking is not taught and kickboxing does not teach throws, grappling and breaks (though clubs may vary what they teach).

Many self defence clubs run courses or seminars and don’t grade.  You don’t become a black belt in self defence you simply become proficient.  And you normally train in everyday clothes i.e. tracksuit and trainers rather than a gi or uniform.