As a Noun:
1. A recurring period of time (such as a week, month or year) before the time of speaking. The unit of time has already been mentioned. English = this week, this month, this year, etc.
2. The used up or elapsed time within the unit of time (week, month, year, etc.) being talked about; this past week, this past month, this past year, etc.
1. Used at the beginning or end of a sentence, or immediately next to a verb, to mean the action takes place sometime during the previous unit of time being talked about, or before some other reference time.
2. English = earlier during this week (month, year, etc.), earlier during that week (month, year, etc.).