Other forms: yogis; yogin
In the western part of the world, a yogi is someone who practices yoga, the physical and mental discipline of meditation and body postures. Do you do sun salutations every morning? Then you're a yogi!
The word yogi comes from a Sanskrit root, yuj, which means "to join or unite." This ancient source never meant "doing yoga poses," but referred to a deeply mystical practice. In India, a yogi can be a spiritual practitioner of various kinds, but in the West, it's come to refer to someone who does physical yoga asanas, or poses with names like "cat," "cow," and "downward dog."