What is the "MULT" means? How can I use this visa for more than 2 entries to Schengen area?

Question

I have applied for a tourist visa (first time) in the Netherland Embassy year 2012, I was given "01" entry for 90 days and exit from Schengen area when my visa expired. After a year, I decided to apply again for a tourist visa, and unexpectedly granted a "MULT" which means I can go back to Schengen more than 2 entries. My visa is valid from June 6, 2014 - June 6, 2015 (1 year). I had my flight going to The Netherlands on June 9, 2014 and exit on September 6, 2014. I am a bit confuse about the "180 days" policy, which I really don't understand. If I will spend 90 days in Schengen and exit for 90 days before i will be able to go back, I can only consume my "MULT" entry for twice, because we only have 365 days in a year. My question is, What if I exit from Schengen 2 weeks before the end of my 90 days, and stay at my resident of country for only 2 weeks and re entry again?

70 days consumed, then exit.
2 weeks in my country, then re entry again.

Answer 1

Number of entries and duration of stay are entirely separate. Leaving and entering does not open any right to stay longer but the 90 days need not be spent in one go, except if you have a single-entry visa.

With a one-year multiple-entry visa it is indeed impossible to stay more than six months or so in total but you can enter and leave as many times as you want. So you could enter, stay a few days, leave for a week, come back, etc. as long as the total stay in the last 180 days never reaches 90 days. That would not be possible with a single-entry visa, even one that is valid for a few months and has a maximum stay of 90 days.

In your case, if you spent 70 days in the Schengen area and went back to your country of residence, you have 20 days left. If you reenter after two weeks, you can still spend those 20 days in the Schengen area. But you do not get another 90 days immediately, that's how the 180-day rules matter.

You can find more info about the duration of stay rule in How does the Schengen 90/180 rule work? and links to a calculator at How to calculate stays against 90/180 visa rules?