浪漫 is a phonetic transliteration of the English 'romantic' (via Japanese). The characters were chosen for their flowing, free-spirited meanings, which fit beautifully.
usage
浪漫主义 (làngmàn zhǔyì) means 'Romanticism' - the literary/artistic movement.
register
In the sense of 'fanciful' or 'unrealistic', 浪漫 carries a literary flavour and is far less common than its everyday meaning 'romantic'.
