Adb sideload is a feature in recovery (e.g. ClockWorkMod) that allows you to flash packages directly from your computer instead of copying them your sdcard.
Boot into CWM (from my signature), select 'install zip from sideload', plug in usb and write in terminal 'adb sideload zipname.zip'.
You also need to have the latest adb from jellybean sdk installed on your computer. You can use 'adb devices' in terminal to verify that adb is correctly in sideload mode. It should say 'CWM-Blade sideload'. If it says 'CWM-Blade recovery' instead, you can try restarting adb, unpluging/repluging usb or rebooting recovery.