Darshana is one of three terms in classical Indian language that can be roughly translated to what today's English speakers understand as "religion."
The darshana of yoga is thousands of years old. The system and teachings of yoga darshana were codified and organized by Patanjali into the Yoga Sutras. Patanjali was not the creator of the science of yoga, nor was he the first yoga teacher. However, he was the first that systematized and collected this darshana into one writing.
Darshana is a system through which one can see reality, which is a yogi's ultimate goal. In yoga darshana, just as one can see one's self in the mirror, one can see the true Self through yoga and the Yoga Sutras.