When you "subscribe" to a mail list (AKA e-mail list, mailing list or discussion list) you are electronically putting your name and e-mail address on a list that contains other peoples names and e-mail addresses. You are then a "member" of the list. When any member posts (or sends an e-mail message) to the list address all the members of the list receive the message and discussions are conducted in this fashion with other members replying to the post (or e-mail message) at the same list address.
There are generally two addresses for each mail list. The first being the "administrative" address, where you would send commands, such as the subscribe and unsubscribe commands. The second address is the list "posting" address and is used only to send messages or "posts" to the other list members.
An "open" list means that anyone is able to subscribe, while a "closed" list means that you will have to be approved by the list owner. There are also moderated and unmoderated lists. "Moderated" means that the posts you send to the list go first to the list owner to be approved, if the post is approved the list owner then sends the posts on to the list members. An "unmoderated" list means that as soon as you post to the "list posting" address your post or message goes out to the rest of the members. loveacop is an unmoderated list.
The two most commonly used mail list managers are listserv and majordomo. These are computer programs that manage the mail list you subscribe to.
Mail lists are not the same as Usenet groups or bulliten boards.