Thanks for your reply - it seems to be a te coined by a knitter called Rachel John where you use multiple balls of yarn at the same time (from 2 to 1000!) and very large needles (I have 19mm to start but have seen people knitting with PVC piping).
I've actually bought a Rachel John kit from eBay with 19mm needles and several balls of yarn to make a scarf - it seems it really is as easy as knitting normally but with lots of strande together.
What I'm really interested in is finding some super, mega uber thick yarn to knit with to make some blankets - I've seen blankets like this for sale but can't find any of the raw materials. The woman on YouTube who knits the 'giganto blznket' with plastic pipes says she's using 'wool roping' but no idea where you could get this from.
If anyone is interested in this, there's also a book available called Big Stitch Knitting which looks good.