what is a 29er?

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Are the wheels same/different from 700c?
what is the purpose?

I am not a mountain bike guy.

A "29er" refers to a wide 700c (622 mm) wheel/tire as well as the actual bike that the wheel fits on.

http://www.mtbr.com/29er/

A "29er" refers to a wide 700c (622 mm) wheel/tire as well as the actual bike that the wheel fits on.

http://www.mtbr.com/29er/do mtb 29er use same gearing as standard mtb? (gearing would be bigger)

do mtb 29er use same gearing as standard mtb? (gearing would be bigger)
Typically, yes.