I don’t know about that. I just asked because after performing the partition update, for the moment you can’t flash the provided recovery anymore (see here for details). That’s why I would reccomend not to do the partition update atm.
ADB stands for Android Debug Bridge and is a part of the Android SDK (Software Development Kit). It’s a software that provides direct communication between a pc and an Android device allowing to transfer files, access the system or run commands on the phone. It is a command line tool (but very easy to use), which was originally intended for sofware developing (esp. debugging, hence the name). One of the many functions of ADB is to flash a recovery or update.zip to the phone directly from a pc (that’s what the “apply update from ADB” option in the recovery is for). I just brougth it up in case you didn’t had a sd card.