Job Applications: Applying on Promotion

Hi All - I did search for this topic first, but I couldn't find an answer.

I'm applying for jobs as an internal person for the first time, and I keep seeing the question 'Are you applying on promotion?'.

What exactly does this mean? I tried to Google it, but it didn't give a clear answer, suggesting it was something to do with finishing probation or same-level job applications, which for me isn't what a 'promotion' is.

Or is Google just being screwy and it is just what it says, you're apply for a higher level job?

Many thanks in advance for any information - I just want to ensure that I'm choosing the correct option.