What does %* mean in a batch file?

One important point not listed in any of the previous answers: %* expands to all parameters from the command line, even after a SHIFT operation.

Normally a SHIFT will move parameter %2 to %1, %3 to %2, etc., and %1 is no longer available. But %* ignores any SHIFT, so the complete parameter list is always available. This can be both a blessing and a curse.

It means "all the parameters in the command line".

For example, it's useful when you want to forward the command line from your batch file to another program:

REM mybatchfile.cmd
echo You called this with arguments: %*
echo I will now forward these to the DIR command.
dir %*