Hi Green light, this is a polite way of describing a job that doesn't have a lot of status.

a low-quality and a low-level job. It's not necessarily a badly paid job because there are low-quality and low-level jobs that are well paid. :)

Cherry gave a great definition. You can also use the phrase "it's not much of a..." to describe almost anything in the same way. "It's not much of a meal". "It's not much of a vacation".

Hello Green light, This expression refers to the insignificance, smallness or lower status of the mentioned job. It lessens and belittles the quality of the job , the quantity of work done or any other attribute associated to that job done.

It's not much of a job means a small job.