They classify the decimal place of the basic unit. ie, the meter is classified with milli (1/1000), centi(1/100), deci (1/10), Deca (10), Hecto (100), Kilo (1000). So instead of saying 1000 meters, you can say 1 Kilometers.
the six common metric prefixes are deka,mecka,sacka,eeba,hecta,and deci
The main prefixes for metric system are:kilohectadecadecicentimilliThese can be used with meter , gram ,liter.
Prefixes in the metric system are combined to represent certain units. For example, the letter T, which means Tera, represents the number 1,000,000,000,000.
The prefixes are all powers of 10. The main prefixes are milli, centi, deci, deca, hecto, and kilo.
The prefix for 10-9 is nano-.
You can find a list of SI prefixes here: http://en.wikipedia.org/wiki/SI_prefixes#List_of_SI_prefixes