What’s the Difference Between Ad-Hoc and Infrastructure Mode?
 

Not all Wi-Fi networks are created equal. Wi-Fi access points can function in either “ad-hoc” or “infrastructure” mode, and many WI-Fi-enabled devices can only connect to infrastructure-mode networks, not ad-hoc ones.

Wi-Fi networks in infrastructure mode are generally created by Wi-Fi routers, while ad-hoc networks are usually short-lived networks created by a laptop or other device. But it isn’t always so simple.

http://www.howtogeek.com/180649/htg-...tructure-mode/