"Per diem" means that a company hires you part-time and that they only use your skills or services "as needed." You will not receive benefits, but you will have more flexibility. Many nurses, construction workers, pilots, and substitute teachers work by the day. The pros of working per diem are that you have control over how much you work, you can find a schedule that works best for you, and you may have better quality of life. The cons are that you may not have job security; the company could terminate your employment at any time. In addition, you may really want to work more, but there may be no hours (funding) available for you, especially near the end of the fiscal year. The best thing would be to find someone who also works per diem for the company and ask them some questions. Do your research, and you may feel more comfortable taking this type of job!

Take a look at this website from Human Resources MBA.net:

https://www.humanresourcesmba.net/faq/what-is-per-diem-employment/

The phrase "per diem" means "per day" or "by the day."

In terms of jobs, if the position itself is "per diem" it probably means that it is not steady work.  Instead, they will, at best, be hiring you on days when they need you (sort of like substitute teaching would be).

Per diem can also refer to payments that you get in addition to your regular pay.  For example, if you go off to an assignment somewhere out of town, your employer might give you a per diem for food and lodging.

But it sounds like the first definition is more applicable in your case.