What is meant by reaching the nisab and "the passing of a year" in the rulings of zakat?

The nisab is the minimum amount of wealth upon which zakat becomes obligatory; zakat is not due on anything less than it. It varies depending on the type of wealth subject to zakat. The hawl is the passing of a full lunar year while possessing the nisab. Both are conditions for the obligation of zakat, though for some types of zakatable wealth, the hawl is not a condition.