What is a Mouse?
1. any of numerous small Old World rodents of the family Muridae, esp. of the genus Mus, introduced widely in other parts of the world.

2. any similar small animal of various rodent and marsupial familes.

3. a quiet, timid person.

4. Computers.  a palm-sized, button-operated device that can be slid on wheels or ball bearings over a desktop to move the cursor on a CRT to any position, or slid over a drawing in order to recreate the drawing on a CRT.  Cf. joystick.

5. Informal.  a swelling under the eye, caused by a blow or blows; black eye.
6. Slang. a girl or woman.

7. to hunt out, as a cat hunts out mice.

8. Naut. to secure with a mousing.

9. to hunt for or catch mice.

10. to prowl about, as if in search of something.

11. to seek or search stealthily or watchfully, as if for prey.

~ The Random House Dictionary of the English Language

As mentioned above, "mouse" is a very board common name that includes many different genus of rodent in the Order Rodentia and sometimes different genus of opossums in the Order Marsupialia (syn. Didelphimorphia).

There are so many different kinds of mice living in different habitats all over the world and there are so many of us, we can definitely take over the world ~(8:>
Let me tell you a little bit about the type of mice we usually refers to: *Chuu!*

Common name: House mouse
Scientific name: Mus musculus (order Rodentia, suborder Sciurognathi, family Muridae, subfamily Murinae)
Distribution: Spread throughout most of world through its close association with humans; in some areas restricted to human dwellings and habitats maintained by human activity; sometimes feral where introduced.
Body: 6.5 - 9.5cm Tail: 6 - 10.5cm
~Mammal Species of the World (MSW)


But what about "rat"?

Rats!  I knew you're going to ask that....

1. any of several long-tailed rodents of the family Muridae, of the genus Rattus and related genera, distinguished from the mouse by being larger.

2. any of various similar or related animals.

3. Slang. a scoundrel

4. Slang.
    a. a person who abandons or betrays his or her party or associates, esp. in a time of trouble.
    b. an informer.
    c. a scab laborer.

5. a pad with tapered ends formerly used in women's hair styles to give the appearance of greater thickness.

~ The Random House Dictionary of the English Language

One of the Rat species:

Common name: House Rat
Scientific name: Rattus Rattus (order Rodentia, suborder Sciurognathi, family Muridae, subfamily Murinae)
Distribution: Native to Indian Peninsula, and introduced worldwide in the tropics and temperate zone
Body: 20 - 26cm Tail: 20 - 24cm
~Mammal Species of the World (MSW)

So... we mice are basically in the same family with "rats".  They are just our bigger cousins who could be very helpful in world dormination *grins*, but we are the more kawaii one that you're gonna love us and worship us ^_~.