Level II vs Inside Marlet

Hello,

I am a bit confused about the terms Level II and Inside Market. Sometimes it seems Level II is the real depth of the market and sometimes it seems to be only the inside market.
Data providers always refer it to Level II but it is not real Level II all the time. It is not the first time I found this when analyze Level II data. Am I missing something?
How can I distinguish both terms? How can I be sure about the provider offer?

Any help will be much appreciated.

Why bother? Unless you use scalping techniques of the order flow reading and a TT grade platform (or Jigsaw add on) the level II is useless. You will have bid/ask but not the price action with real time trades executed and no total volume traded, no traded at bid or ask, etc.

Level II has nothing you could use in real trading. But it's a very fancy cool thing you must have along the charts and 45 indicators with flashing colors