Unitarian Universalism arose out of the joining together of Unitarian and Universalist Churches in the US. Here is how they describe themselves.
In Unitarian Universalism, you can bring your whole self: your full identity, your questioning mind, your expansive heart.
Together, we create a force more powerful than one person or one belief system. As Unitarian Universalists, we do not have to check our personal background and beliefs at the door: we join together on a journey that honors everywhere we’ve been before.
Our beliefs are diverse and inclusive. We have no shared creed. Our shared covenant (our seven Principles) supports “the free and responsible search for truth and meaning.” Though Unitarianism and Universalism were both liberal Christian traditions, this responsible search has led us to embrace diverse teachings from Eastern and Western religions and philosophies.
Unitarian Universalists believe more than one thing. We think for ourselves, and reflect together, about important questions:
The existence of a Higher Power
Life and Death
Inspiration and Guidance
Prayer and Spiritual Practices
We are united in our broad and inclusive outlook, and in our values, as expressed in our seven Principles. We are united in shared experience: our open and stirring worship services, religious education, and rites of passage; our work for social justice; our quest to include the marginalized; our expressions of love.
A more detailed explanation can be found here.