"Ham Radio" is a term used to describe the activities of licensed amateur radio operators. In general, it covers the activities worldwide of individuals whose hobby involves non-commercial radio operation and electronics, governed by both national and international rules and restrictions. In the US, all ham radio operators must obtain a license to operate from the Federal Communications Commission (FCC).
Although the origins of the term have never been positively identified, in the early days of radio many experienced wired telegraph operators were hired to be the first commercial wireless operators. It is believed these seasoned key pounders looked down upon the upstart amateur operators and because of their perceived poor telegraph skills, insultingly referred to them as “ham fisted”. Some believe it originated with the pronunciation of "amateur", which sounded like "hamature" then was shortened to just "ham".
The true meaning of HAM stand for is unknown but it has two popular versions. The first one is said to have been taken from early amateur radio operators who took the first initials of 3 people who had made great strides in experimenting with radio. The second story was said that in the early days amateur radio operators frequencies were very limited so all the frequencies they can use were so sandwiched next to one another it was like a ham sandwich. For more information, look here: http://www.qsl.net/vu2msy/MEANING.htm