Other: This is RAM that is unavailable right now because it's in use by services that are actually running (it might be ones that can't be killed, in fact). Using your example, there's 78 MB of RAM in use by 4 processes, hence "78 in 4".
Avail: The first number here is the amount of RAM that is completely free and not allocated to any process (the 109 MB in your example). The second number is allocated but the process is in a state where it can be deallocated. Thus, "58 MB in 8" means there are 8 processes that are currently holding 58 MB of memory, but they are paused/frozen in the background and that 58 MB can be reclaimed by the OS if an active process needs it.
Edit: As Jake pointed out in the comment below, you can find a description in this entry on the Android Developers Blog (scroll all the way to the bottom).