It's a common expression used to express remorse, sadness, or disappointment about something.
Here are some examples:
* Je regrette de ne pas avoir pu venir à ton anniversaire. (I regret not being able to come to your birthday party.)
* Je regrette de t'avoir blessé. (I regret hurting you.)
* Je regrette ce que j'ai fait. (I regret what I did.)
It's important to note that "je regrette" can also be used in a more formal context, such as when expressing condolences or apologizing for a mistake. In these cases, it can be translated as "I am sorry".
* Je regrette votre perte. (I am sorry for your loss.)
* Je regrette de vous avoir déçu. (I am sorry for disappointing you.)