What does the "USM" in Canon lens mean?

[afiend]

As above.

How many types of lenses does canon have. Is there only the 'L' (better) and non-L series?

Thanks in advance. Hope this clears my doubts and paves the way to a new Canon SLR

 

[megaweb]

you can find most of ur answer to ur qns at

http://www.usa.canon.com/eflenses/lens101/glossary/index_a.html

 

[afiend]

Thanks!

 

[ziploc]

USM = Ultra Sonic Motor on Canon lenses. The nikon equivalent is silent wave motor on the AF-S series of lenses.

You can also find more information on USM at
http://www.usa.canon.com/eflenses/technology/index.html
besides the URL given by megaweb.