Mailing list is a group of recipients to whom users can refer by a common name (for example, a mailing list called Linux-Developers). When users address a message to a mailing list, all members of the mailing list receive the message. Specially, mailing list is a group where the recipients have a common stand and thus they subscribe to the list. In Linux community much development effort and bug fixing is done through mailing list and IRC.
Linux mailing lists are easily subscribe-able and unsubscribe-able. You can add yourself to the mailing list any time and remove anytime as you wish. Internet mailing list are ways to communicate ideas, informations and opinions over the internet.
There are many types of mailing lists. Some are really high traffic. That means you will have to sacrifice a lot of mailing space. Some have low traffic and it will be like everyone knows everyone. Some high traffic mailing lists are about kernel and databases. Developer mailing lists and designer mailing lists are also high traffic. You will find localized mailing lists to be having lot less traffic.
When you give cc to the mailing list all the recipients will receive the same email. They all will have chance to talk to you. People interested in a particular field benefit a lot from mailing lists.