conjunction

When something happens, "because" is used to explain why it happened. For example, if you asked why the sky is blue, you might say "because the air in the sky scatters the blue light from the sun."

Example

1. I stayed up late because I had to finish my homework.
2. I'm tired today because I didn't sleep well last night.
3. I'm out of milk because I forgot to buy some at the store.