You won’t be classed as retired if you intend to start another role in which you can build a USS pension (with either your current or a new employer). But if you’re retired and then offered another role, your employer may need to automatically enrol you into a pension scheme. You’ll need to speak to your employer about whether you can re-join USS.
Please note there are certain factors which will affect your pension if you retired due to ill health, but then start working again. Take a look at ill health retirement to find out more.