Critical illness insurance pays out when one of the specified critical illnesses occurs. For example, following a heart attack, stroke, cancer or some other specifically defined critical illness.
Cover is for a set term, which may be equal to a mortgage term, or for when children have grown up, until retirement, or until another life stage milestone is achieved. It may be worth considering having one policy for a set term to cover the mortgage and another that will provide money to help provide for your different lifestyle if a serious illness happens.
Most people choose a lump sum to be paid out. There is the option of receiving the payout as a set income over the term remaining, which is often a lower-cost option.