What is a militant atheist?

Miltant atheist

http://a7.vox.com/6a00fad6aef25f00050123f174863786...

Militant as an Adjective can mean "vigorously active and aggressive, especially in support of a cause" as in 'militant reformers'. Atheist can be militant in their non-beliefs

I would say "militant atheist" is a derogatory term for "aggressive atheist"... and for a good example of that, I would recommend a video from Pat Conell, such as linked below. These atheists speak frankly and unkindly of religion. However, they are not "militant"... they are not whatsoever violent physically, though maybe verbally.

Examples of militant atheists are Lenin, Mao, Stalin, Pol-Pot.

Someone who wants equal rights under the law as the religious people or wants religious people to abide by the same laws as non-religious people. They are dismissively termed a "militant atheist" to imply they are radical, fringe, or dangerous.

Militant Atheist is usually used to refer specifically to people who think that religion is demonstrably false or nonsense or that it is usually or always harmful.

An atheist that believes there is a war to be waged against theism.

An atheist on the warpath against theism.

A nutty atheist that takes his atheism way too seriously.

An atheist who tries to force atheism on others. The same can be applied to a Christian, a Muslim, a Jew, etc. However, it's almost always applied to atheists.

they are the ones who preach