Walk me through the difference between a bond's Coupon Rate and its Yield to Maturity (YTM). What does each rate represent, and under what circumstances would they be equal or different?

作为一名在资本市场工作的专业人士，请你解释一下债券的票面利率（Coupon Rate）和到期收益率（Yield to Maturity, YTM）之间有何区别？这两种利率各自代表什么，以及它们在什么情况下会相等或不同？