artemiso 

It's an outdated terminology and I dissuade using it because of its inconsistent application and the amount of context you'll need to provide when using it in any communication.

I wouldn't say its outdated; rather is a tad more 'general' these days as opposed to the specific definitions we had 2 decades ago. From a programmatic/API implementation perspective, I do agree with your definitions table above though

For many years, L2 was 'somewhat standardised' to be 5 or 10 levels.

It was the exchanges offering more data services, and then ECN's & data providers that started changing definitions around what L2 offers (MBO, MBP), and then coining terms as L3 and more (which actually goes far deeper) which caused some minor confusion.

In simple terms:
L1 = Top of Book
L2 = Typically 5-10 levels depending on provider (in some cases i.e Rithmic, much more). MBP
L3 = All above, MBO + much more (all individual orders, messages, fill probability and fill rates, queue dynamics, rest times). Many are also now customisable, and I've used one provider that offers predictive queue analytics/capability.

Again, some providers have skewed L2 a little by merging what was traditionally L3 into the L2 space. But for the most part, the definitions above are what most industry professionals refer to and know of.

Trading off from a chart or using technical analysis with it to place entries and exits, you won't need Level 2 market data since Level 1-aka-Top of Book provided free by your brokerage firm is good enough. In case your taking the less travelled road, ie. learning Order Flow (also called Depth of Market-DOM or price ladder), then yes ... you need subscribe to Level 2 data and pay a monthly fee for it.

While considered Order Flow, would a footprint chart just need L1, because it is only looking at actual trades and not the order book?

Sent using the NexusFi mobile app

answering to earlyrun's question, all platforms i know require level 2 data in order to display a footprint chart. If you can be resourceful you may find a workaround to that, but i don't think it would be worth your time given that l2 data doesn't even cost that much

thecrispins 

answering to earlyrun's question, all platforms i know require level 2 data in order to display a footprint chart. If you can be resourceful you may find a workaround to that, but i don't think it would be worth your time given that l2 data doesn't even cost that much

Level 2 is not required to display the footprint tool. With Ninjatrader for example, just top of the book aka L1 data is necessary. It is logical since the footprint uses executed orders not advertised orders which belong to level II data.