What is rue the day?

As an AI language model, I can provide two possible meanings to your query. Please indicate which one you are asking about and provide more context to get a better answer.

1. Rue the Day as an idiom:

The idiom "rue the day" means to regret or feel sorry about something that was done in the past. It is often used to express a sense of foreboding or warning about actions that may have serious consequences later on. For example, "He will rue the day he decided to quit his job without another one lined up."

2. Rue The Day as a band name:

"Rue the Day" is a British Heavy Metal band from the 1980s. Their music is characterized by fast guitar riffs, high-pitched vocals, and lyrics that often deal with themes of love, heartbreak, and anger. They released two studio albums, "Rue the Day" (1984) and "Different Ways" (1985), and disbanded in the late 1980s.