What does incidence rate ratio mean in this specific case?

"Poisson regression models were used to estimate the suicide incidence rates and incidence rate ratios (IRRs) along with their 95% CIs within each targeted age group."

The tables give the IRRs as numbers like 1.005 and 1.007, but I don't understand what the numerator and denominator are supposed to be.

Study name - "Association Between the Release of Netflix’s 13 Reasons Why and Suicide Rates in the United States: An Interrupted Time Series Analysis".
^ pasting this into Google should immediately show you a PDF link