Different type of Dates in SAP PM?

Dear Gurus,

I saw different types of dates in SAP PM like Basic start date,Basic finish date.....

Could anybody elaborate what exactly the significance of different below mentioned dates. I searched some links but i cannot get my exact requirement.

1. Actual Start Date.

2. Actual End Date.

3. Basic start Date.

4. Basic Finish Date.

5. Scheduled Start Date.

6. Scheduled Finish Date.

Regards,

Harsha.