You can think of prana as "life force." In yoga, the word "prana" is used, but the same concept is present in many forms of philosophy, religion and medicine that arose in the Far East. In Chinese medicine, it's called "chi" or "qi." In some forms of Buddhism, it's translated as "energy wind" or "inner wind." Regardless of what it's called, moving, strengthening and cleansing our prana is one of the primary goals, if not the primary goal, of yoga, not to mention the goal of Tai Chi, Qigong, acupuncture, Reiki, certain forms of massage and certain meditative practices.
The cost of in person instruction also includes hidden costs that must be added to the tuition cost of the training course. Hidden costs would include the cost for tutoring, study materials, membership, application, enrollment fees, and other hidden fees that the institution may choose to include. You do not have these additional hidden costs with online Yoga training.
A true Guru, Swami, or Yoga master does not present him or herself as such, instead the yogi or yogini's level of accomplishment would be evident through his or her behavior, understanding, speech and affect on other people. According to Indian tradition, a true Yoga master would also be a disciple of a long lineage of authentic Yoga masters, stretching far back in time, even as far back as Shiva. A true Yoga master would also usually have a group of dedicated initiates following his or her teachings.