In Schema level we can say as when we consider these as Count of Occurances/even that does not involved or getting aggreaged at the fact table means,we call these fact(has no measure but with events/occurance) called as Fact less Fact table.

for eg. No :of Accident for a Months
           No : of Policy has been closed this months.

Generally we  using the factless fact when we want events that happen only at information level but not included in the calculations level.just an information about an event that happen over a period.