What does "@" mean in Windows batch scripts

It means not to output the respective command. Compare the following two batch files:

@echo foo

and

echo foo

The former has only foo as output while the latter prints

H:\Stuff>echo foo 
foo

(here, at least). As can be seen the command that is run is visible, too.

echo off will turn this off for the complete batch file. However, the echo off call itself would still be visible. Which is why you see @echo off in the beginning of batch files. Turn off command echoing and don't echo the command turning it off.

Removing that line (or commenting it out) is often a helpful debugging tool in more complex batch files as you can see what is run prior to an error message.

It means "don't echo the command to standard output".

Rather strangely,

echo off

will send echo off to the output! So,

@echo off

sets this automatic echo behaviour off - and stops it for all future commands, too.

Source: http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/batch.mspx?mfr=true

By default, a batch file will display its command as it runs. The purpose of this first command which @echo off is to turn off this display. The command "echo off" turns off the display for the whole script, except for the "echo off" command itself. The "at" sign "@" in front makes the command apply to itself as well.

The @ disables echo for that one command. Without it, the echo start eclipse.exe line would print both the intended start eclipse.exe and the echo start eclipse.exe line.

The echo off turns off the by-default command echoing.

So @echo off silently turns off command echoing, and only output the batch author intended to be written is actually written.

It inherits the meaning from DOS. @:

In DOS version 3.3 and later, hides the echo of a batch command. Any output generated by the command is echoed.

Without it, you could turn off command echoing using the echo off command, but that command would be echoed first.