Define Romanticism and elaborate on the characteristics of Romantic poetry?

The term Romanticism is most often applied to the British poets of the late 1700s to the early 1800s, including William Wordsworth, Samuel Taylor Coleridge, John Keats, and Percy Shelley, to name a few.
The characteristics of Romantic poetry include a focus on the individual, love of freedom and liberty, an appreciation of the natural world, and an interest in mystery and the supernatural. In some ways, the Romantic period of literature can be seen as a response to the Age of Reason of the 1700s. The Romantics embraced the supernatural and the strange, while Enlightenment thinking argues that "mysterious" phenomena can be explained and understood through logic and reason. However, Romantics did not necessarily eschew the real world around them in favor of fleeing into a fantasy world. Take one of the Romantic novelists, Mary Shelley, for example. Her masterpiece Frankenstein is a condemnation of the excessive ambition of humans who cross the line and try to play God or take natural processes into their own hands. The novel, of course, involves the supernatural and is one of the first Gothic novels (Gothic, as a genre, is sometimes referred to as Dark Romanticism). The Romantics were supporters of revolutions that resulted in individual liberty (for example, the French Revolution), so they did have political stances. 
One of the most commonly referenced characteristics of Romantic poetry is its frequent depictions of nature. Poems that feature the speaker's love of nature can also engage with political contexts though. For example, Wordsworth sometimes included critiques of the Industrial Revolution in his poems that seem to be ostensibly about the beauty of the natural world.
These are not necessarily the only features of Romanticism, but interest in nature, the individual, and the supernatural are a few common denominators in Romantic poetry.