Decreasing Cover
The amount of cover that was taken out at the start will reduce over the term, so that at the end of the term the amount of cover would be zero. This is usually arranged alongside a repayment mortgage, the balance on the mortgage will reduce over the term so at the end of the mortgage you'll not owe anything. In times of high interest rates, you need to regularly review your cover to ensure that it will fully redeem the mortgage should you need to claim.
Level Cover
The amount of cover that was taken out at the start will remain the same over the term of the cover.
Increasing, or index linked cover
Increasing cover, also known as index linked, adds an annual increase to the amount of cover you have. This does also comes with an increase to the premium though. This is applied to ensure that the effects of inflation don't reduce the amount of cover in real terms. This type of increase typically applies to covers like income protection, or family income benefit, which are usually taken out to maintain a standard of living. Without anti-inflationary increases, the amount of cover may not be sufficient to cover all costs in the future.