Ok, if you mean something like this (like it's present on IMDb by default):
then miniBB stands for a mini-board where
only the most popular and the most comfortable to read presentation of messages is given.
I'm not quite sure why do you call this mode a "tiny" mode?
How could you describe it's comfortable in use?
For me it's quite a big time to click on each message to see what it is about, if all messages almost always behave on the same subject. When all messages are scrolled from top to the bottom, it's a native comfortable reading.