Is the date on cheerios cereal bar a sell-by date or expiration date?

Not neccessarily. Anyway, much of the time you can ignore the expiry date - food is usually ok for several daysafterwards.

Normally, the sell by date also gives the consumer a short amount of time(minimum) to consume the good.

In most cases (all?), yes, it is.

No

Well, on the day after the expiration date, it should still be OK to eat. Just don't wait a week or so to eat it again because it will turn moldy and sticky .