An expanded range. Extended communities are 8-bytes wide, whereas regular communities were only 4-bytes wide. So, this ensures that extended communities can be assigned for a plethora of uses, without the fear of overlap.
The addition of a 'Type' field provides structure for the extended community
Route Target (RT)
Site Of Origin (SOO)
Although these two community types are generally used in L3 VPN network setup, you can also use them in a non-L3 VPN network to control the distribution of BGP routes.
BGP does not send either the extended or standard community attributes to their neighbors by default; you must use the configuration command configure bgp neighbor send-community.