What is the theta of a bond?

Could you please explain what is meant by the term "theta of a bond" in finance? I'm trying to understand the significance of this metric in relation to bond pricing and risk management. Could you elaborate on how theta affects the sensitivity of a bond's price to changes in time? Additionally, is there a specific formula or method used to calculate theta for a given bond? I'm interested in learning more about this concept and how it can be applied in practical financial analysis. Thank you for your assistance.