These are my definitions … if you want to official thing, go grab a dictionary.

Batch sparge – dumping the sparge water (see below) all at once, rather than a slow trickle as is done with the fly sparge method

Mash Tun – Insulated container used to mash grains

Mash – steeping grains to convert starches to sugar

Mashing in – mixing crushed grains and strike water in the mash tun

Strike water – water added to the mash tun to start the mash process

Sparge water – water added to the mash tun after the initial wort has been drained to help remove additional sugar left in the grain

SG – Specific gravity, a way to measure the sugar content of a liquid

Wort – liquid mixture of water and sugar from grains before fermentation turns it into beer