Annum means year, but you'll almost never see it standing alone. It appears in the Latin phrase per annum, which means “for each year” or “yearly.”

When someone says an investment grows at 5% per annum, they mean it increases by 5% every year. If a job pays $50,000 per annum, that's the yearly salary. The phrase shows up often in banking, business, and legal documents because it sounds more formal and precise than simply saying “per year.”

You might wonder why people use a Latin phrase instead of plain English. Sometimes per annum appears in official contexts where precision matters, like contracts or financial statements. Other times, people use it simply because it's traditional language in those fields.

You can see the same root in annual (happening every year), anniversary (the yearly return of a special date), and annuity (a payment made each year). But when you see annum itself, it's almost always paired with per to mean “each year” or “yearly.”