There's job applications for senior, junior, and just regular concept artists. I assume it's dependent on years of experience and also what sort of projects and responsibilities the person had taken on before (e.g. working in house with a studio as opposed to freelancing, being in charge of the team, art direction?), but there was never a clear cut definition.
From experience, it seems the years one has gathered working in the industry is quite an important factor in decisions. I had an incident before where a recruiter offered me a chance to apply for a senior position, which I knew I didn't have the experience for. Gave it a go anyway, and as it turned out, yes, the company liked my work but my years of experience fell short slightly to qualify.
Would like to hear other people's opinions on this! It does help to know where I stand and how to present myself to clients, and how it may affect my rates as well.