The word apology can be used in a few different ways. You might say I'm sorry to apologize for something you did wrong. For example, if you accidentally bumped into someone, you might say I'm sorry to apologize. Alternatively, you might use the word apology to describe how regretful or disappointed you are about something. For example, if you found out that a friend was moving away and you weren't able to say goodbye, you might say I'm so sorry.