A train hopper is someone who travels by hopping onto freight trains, usually without paying for a ticket. The term 'HOBO' is often used to describe this type of traveler, as it is a four-letter word that is derived from the phrase 'homeless bohemian'. Train hoppers typically travel long distances and often live on the road for extended periods of time. They may also engage in activities such as scavenging for food or money, or engaging in other forms of work.