What is Amateur Radio or Ham Radio?
Definition from Wikipedia: Amateur radio (also called ham radio) is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication. The term “amateur” is used to specify persons interested in radio technique solely with a personal aim and without pecuniary interest, and to differentiate it from commercial broadcasting, public safety (such as police and fire) or professional two-way radio services (such as taxis, etc).
The American Radio Relay League is the national association for Amateur Radio in the USA. http://www.arrl.org/what-is-amateur-radio
Guide for new hams: http://www.eham.net/newham/
Amateur Radio and Emergency Communications: https://alertfind.com/amateur-radio-and-emergency-communications/ (Link suggested by Skylar Gray)
The best way to learn about amateur radio is to join a club!