To more directly answer your question Balphina,

Outer Range: When a muscle is in a lengthened state. I.e. standing and flexing knee as far as you can (quads stretch) will put your quads @ outer range. Generally in its outer range, the muscle is on stretch!

Middle range: Point which your muscle is generally at its best length-tension relationship . i.e. your forearm bent to approximately 60 degrees has your biceps @ around middle range. (length is between inner and outer range)

Inner range: When your muscle is @ it's shortest length. I.e. flexing your shoulder (> 90 degrees) and flexing your elbow (as much as you can) will put your bicep @ its Inner range.

Understand that your muscle isn't only @ its outer/inner range when it hits it's shortest/longest possible length, these are "zones" we use to describe the muscle length. So you could well argue when your shoulder is not flexed, and you bend your elbow to 160 degrees that your biceps is in "inner range". Generally if you are describing a muscle position, using the muscle "range", it is generally a good idea to also give joint position information for a clearer picture, if talking generally, you can mostly just use the muscle "range".

As gcoe explained, knowing about your muscle ranges is very important in understanding length-tension relationships and in describing muscle positions, patterns etc.