Radio
A radio is comprised of the songs a listener has featured, saved or tagged. Other listeners “bump” each other's radios, to increase the listen count of that user. It's a fun way to find good music you may have otherwise missed, and you can help other people get the Disc Jockey achievements at the same time.
Every group also has a group radio, which is comprised of all the songs listed on the group wall, as determined by the group members' hearts/saves/features.
Radio Bumps
As mentioned, listeners can “bump” each others' radios, to help that listener earn a level of the Disc Jockey achievement, and/or as a requirement for the Radio Surfing quest.
When you click on the “listen to radio” link on a listener profile page, their listen count will increment.
Note: While you can click “listen to radio” as often as you like, you cannot bump any other radio for 5 minutes after bumping one. You do not have to be listening to the radio for 5 minutes for the bump to register, it will register at the click.
Thesixtyone has developed an etiquette for radio bumping that includes leaving a post on the listener's wall telling them you've done so, usually including the bump number (typically the “listens” count, plus one, unless you've already refreshed their profile page 1) ), and what song you got. For example:
RB#667 = Bankai - PARTY HARDER
Cheers, and party harder man!
It is also customary to greet new members to a group with a “welcome wagon radio bump”.
TIP: Sometimes, it seems that a radio bump won't take effect. In this case, a common trick to ensure that the bump is counted is to click on the “listen to radio” button 3 times. (hat tip to listener QuixoticNeurotic for this hint)