Some definitions (more formal definitions are available)

European Union (EU)

The European Union (EU) is a political and economic union of 28 member states that are located primarily in Europe.

European Economic Area (EEA)

The European Economic Area (EEA) is the area in which the Agreement on the EEA provides for the free movement of persons, goods, services and capital within the European Single Market, as well as the freedom to choose residence in any country within this area.

It is quite possible to be a member of EEA while not being a member of EU.

The Referendum Question

Should the United Kingdom remain a member of the European Union or leave the European Union?


So, we know the referendum was close (48.1% vs 51.9%) and we also know the result was not legally binding. But please note: even if the Tories or any other "Brexit means Brexit/will of the people" flavoured party wants to take us out of the EU there was no referendum on leaving the EEA. Consequently...

any negotiations to take us out of EU that include us leaving EEA will be undemocratic, non-constitutional and illegal.