Some of you seem to have very strong (and I think rather harsh) opinions on this. How many have actually read the seminal text, A Theology of Liberation (Fr. Gustavo Gutiérrez), from which this school of thought gets its name?
In answer to the original question, liberation theology basically refers to a very broad theological/political movement emphasising the causal connection between sin and social injustice, and the role of the Church in fighting these evils. It arose largely in response to acute problems of economic and political oppression in latin america during the second half of the C20th. Gutiérrez's work was important and lent the name 'liberation theology'. While it's possible to discern the influence of Hegelian and Marxist concepts in his work, to say that therefore the whole movement is 'Marxist' or 'Communist' is facile and immature. It also drew heavily on biblical prophetic literature and the ideas of earlier C20th catholic social thinkers.
Many priests, nuns, religious, catechists and missionaries were martyred during the 1980s, having been inspired by the Christian ideals of liberation theology. Others showed tremendous courage faced with threats of death, torture, and rape, in order to bring the sacraments (and Yes, activism as well) to impoverished corners of the world. Posters might wish to remember that before dismissing the movement as 'feces'.
Peace,
FS
Fleetingshadow, rise above your name.
Overthrowing governments is not the job of a priest. What are they doing being priests?
"Christian ideas of liberation theology"? My goodness, what church have you been attending?
A priest must take care of souls. Guide them, baptize them, marry them, give them Communion and the other sacraments.
I think you are dismissing the nature of Christ's Church on earth. Real priests have been martyred wearing a cassock, not machine guns.
With your above statements, you give dishonor and mock the earthly memories of martyrs.
Priests are not revolutionaries. Except in the mind of some sick, twisted perverse minded people.
Get your head out of the NO sermons and into the One True Church. It's not too late.

Thanks Cooler King. A few points:
Firstly, I don't believe I am 'dismissing the nature of Christ's Church on earth. Of course evangelisation and the sacraments come first. This is the primary role of priests above all. But there is no either/or when it comes to spiritual and corporal works of mercy.
Secondly, opposition to severe social injustice does not simply equate to support for war or revolution (however these may be justifiable in specific circumstances according to traditional just war theory). Blithely conflating the two does injustice both to those who work peacefully for social justice and to the Church's balanced approach to difficult questions of political violence.
Thirdly, if you think the only religious killed in El Salvador, for example, were 'wearing machine guns', you really need to do some research, with all due respect. Irish-American nuns who are kidnapped on the road to their rural mission, raped, tortured, and murdered, are martyrs. An archbishop of the Church who is slain at the altar while offering the sacrifice of Calvary because he had called on government soldiers to obey the higher Law and cease mistreatment of the poor, is a Martyr. If that word is to have any meaning, Cooler King, these people are martyrs. Honouring them 'dishonours' no one. One would need to be quite blinded by political prejudice not to acknowledge that.
Finally, I agree with you that NO sermons often leave much to be desired! On that subject, I never heard a sermon on this topic in all my years attending the NO mass. ;)