In Latin terminology, the word "circa" means "around" or "about." The word "per" in Latin roughly means "through" and indicates a period of time. For example, "permanent" means to last indefinitely, while "persist" means to continue for a period of time. You might find these words used in a job search from time to time.
When They're Used
In a job posting, you might see a job salary listed as something like "circa $30,000." That means the job pays around $30,000, though it doesn't necessarily mean you're going to be earning that amount. Your qualifications could mean you'll earn slightly more or less. If you see the phrase "per circa," it's the same idea. If the phrase is followed by the word "annum," or "per annum," you can take that to mean the salary named is the rough estimate per year. If it's followed by "monthly" or "weekly," the salary named is roughly the monthly or weekly amount.