Whether it's self defense or proffesional MMA fighting it's good to have a clear understanding of the 5 different ranges of non armed combat that can take place. I've tried to come up with a classification based on traditional martial arts and MMA as following...

Long range

The long range means your opponent or attacker cannot reach you with the longest weapon of his body while standing still. The longest weapon of your body is usually the side kick or the front kick. If your opponent wants to reach you he has to take an additional step or steps.

The long range is the time where you try to de-escalate the situation if possible. Once your opponent comes inside your kicking range it's time to mentally prepare to attack or defend yourself. Shit could hit the fan at this point.

In Wing Tsun they referred to the long range as critical distance. Once your opponent gets inside your critical distance it becomes critical :)

Kicking range

Kicking range is the range where your opponent can reach you with his longest weapon - the side kick.

side kick

With training you won't need eyes to determine the kicking range, you're just goint to be able to feel it.

Punching range (also takedown range)

Punching range is the range where your opponent can reach you with his longest punch which is the straight punch.

right straight

When you add wrestling to the mix the punching range also becomes the takedown range. If you can reach somebody's face with your arm than you can also reach for somebody's legs with your arms. Wrestlers are able to shoot for a single leg takedown from punching range.

Single leg takedown

Medium range (clinch range)

Medium range is the range where you punches and kick become less effective since you cannot fully extend them because the distance has been shortened so elbows and knees come more into play here.

A good definition of medium range is:

"An intermediate distance where only the knees & elbow - shorter parts of the upper limbs & lower limbs can reach the opponent."

Jon Jones elbowing Rashad Evans in medium range

Wanderlei Silva unleashing knees on Rampage Jackson

This would include knees, elbows, from muay thai and trapping from wing chun.

Close range (first grappling range)

I would define close range as the moment you and your opponents bodies are locked together in the stand up position and you can't use any strikes except maybe a headbutt and it all comes down to grappling (wrestling, judo throws, bjj) to get the opponent to the ground.

Fedor Emilianenko judo throws Frank Mir

Ground range (second grappling range)

Most fights end up on the ground and there wrestling, bjj dominate. Of course you can use ground and pound, elbows as well. Outside of sports competition anything else goes as well; biting, scratching etc.