Acronym that stands for Rooster Teeth / Achievement Hunter. Rooster Teeth is a production company that makes web-based content. They are most well known for their series Red vs. Blue and as well as RWBY. Achievement Hunter is a division of RT that makes gaming/let's play content and streams regularly. If someone says they are an "rtah fan" it just means they are a fan Rooster Teeth and Achievement Hunter.
by chungschwa January 08, 2021