What does as mean in these sentences?

1. As they live near us, we see them quite often.

2. Kate slipped as she was getting off the bus.

3. As I was tired, I went to bed early.

4. Unfortunately, as I was parking the car, I hit the car behind me.

5. As we climbed the hill, we got more and more tired.

6. We decided to go out to eat as we had no food at home.

7. As we don't use the car very often, we've decided to sell it.