Web 2.0 look ?

what is this "web 2.0" look & why is it so special ??
so far all the web 2.0 logos I've seen look flat , with no depth or effects on text what so ever , very simplistic and the colors used are repetitive , like almost all I've seen had blue or orange
some basic details about it , why it is used & how it can be achieved would be useful
thanks !

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