Speed yoga is a term that has been more used lately. Sometimes it's just a way (often joky) of saying that you do the usual yoga poses more quickly - eg you are in a hurry. But there are several modern yoga-based practices that aim to offer the benefits of traditional yoga while giving you more of an aerobic-style workout.
For example, power yoga is becoming very popular - if you click here you will see a choice of video clips, workout instructions etc to give you an idea. Classes like these certainly help you to get fit, and challenge the muscles and increase flexibility, which yoga should do. However, practitioners of traditional yoga would say that this isn't really yoga - you may not get the benefits of calm, mindful time, body awareness and meditation.
To get an idea of how different this type of exercise is from classic yoga, you could look at this video.