Locked Topics (also known as Read-Only Topics, and not to be confused with locked posts) are topics that moderators have locked due to spam, unrealistic actions in Roleplays (OP), flame wars, or other reasons (like being out dated, inappropriate, etc.). At one time, topics were locked due to length, but the mods eventually changed that rule.
Locked Topics cannot be posted in, though posts submitted to the topic before it was locked can still be approved and looked upon. Usually announcements and the like are locked to avoid drawing attention away from the main point of the forum. However, sometimes a glitch will allow Locked Topics to be posted in. In the past, Locked Topics were deleted soon after locking, but nowadays they are not deleted as often.
When a topic is locked, moderators will sometimes let a second topic through with the same idea unless the moderators have requested no more of that type of topic, for example, I LIKE FRODO. This has also happened to Your Position in the MBs, although there is now a new one. Normally the new topic will just have a "2" on the end of it (Or a 3 if the previous topic was a 2, 4 if the last was 3, etc.)." In fact, the topic "Talk to the Mods" in the MB forum, is so popular that it now is on its sixth edition. The topic "Camp MB" has been locked a few times due to spam and off-topic posts.
There have been instances in the past of a topic being locked at a certain point in time, as shown by the old monthly Club Page contests. As stated above, for the most part, when a timed topic was locked, another one was let through, though as with anything, it might not have been by the intended person.
The largest locked topic is the MB Asylum~Roleplay, which was the 4th largest topic at the time of its locking.