It either means it's restarting or you've opted to hide it, in which case it'll pop up when the cursor strays nearby.
I thought you had me on your ignore list? I'm gonna have to go back and edit out all those nasty things I said about you.
Sounds like the dock restarted. But just in case it was just hiding, here's where to turn that behavior off.
i don't have hiding turned on. this 'dock ducking down' isn't related to me moving the cursor nearby, it seems to happen randomly. it dissapears for a second then pops back up. why would the dock restart randomly? this isn't normal is it? what could be causing this?
Delete your com.apple.dock.plist in your preferences folder. It could be that or a malfunctioning widget.
I think you are all going a bit overboard! To antonlamont45: Does this happen alot, or was it just once or twice? The dock goes down and comes back up when you have altered something on the dock, whether it is a setting, or the insallation of a software update. It happens when the dock restarts. Mac OS X will just restart the dock application part of OS X to apply new changes etc. Nothing major, just a part of OS X working Edit: Also, when an error occurs, the dock sometimes restarts, for example, when a program hangs during start-up.
it doesn't happen alot. it might have something to do with application installation, only thing that concerns me is that sometimes when it happens it is followed by a freeze or kernel panic (i can't remember which right now) i will report back with more details if it happens again.
no 3rd party widgets. apps, i'm not sure exactly.. i always have safari and mail open, sometimes itunes and iphoto when this happens.. i'll have to report back with more exact info.
If you're not doing anything at all and the Dock disappears and reappears, then it's likely crashing. How to tell for sure? Open Console.app, click the Logs tile, and check ~/Library/Logs/CrashReporter/ and look for Dock.crash.log. If there is one, select it and go to the bottom and check the timestamp. If it matches with the "disappear/reappearence", then your Dock is crashing and troubleshooting should continue in that vein. If there isn't one, then your Dock isn't crashing and what you're seeing is likely simply "normal" behavior when you're installing or with some app that you've installed.