Permanent residents can lose their status if they don't meet the residency obligation. This means that they can't spend too much time outside Canada. The general rule is that over a period of 5 years, permanent residents must be in Canada for at least 2 years. That's the same as 730 days. The 730 days do not have to be one after the other. And part of a day counts as a full day.
In some situations, permanent residents can include time spent outside Canada. For example, they may be able to include time spent travelling with a spouse or partner who's a Canadian citizen.