How to get a job as a junior developer and what makes you a junior developer?

Recently I have been interested in working with big teams. I have run my programming business/agency for over 3 years and I feel like I need to break away and just learn from the best. However, I would not consider myself as a software engineer because most of the languages I know are self taught. So, thinking of joining a big company and join the dev team as a junior developer might be safer or... am just not sure what and how to classify myself in the category. How do you tell or know you are a junior developer?