An insurance "excess" is the amount you pay towards a claim. So if a claim costs in total £1,000, and there is an excess of £100; you pay £100 as contribution to the claim and the insurer pays £900.
The amount of insurance "excess" will change on your insurance provider. Some are fixed amounts; others allow you to change your excess, by charging you more premium upfront for a lower excess.
There are also different excesses based on the insurance product you buy. For instance, car insurance will have a different excess from a large hotel.
At Dinghy, we have a zero excess on our Professional Indemnity insurance. That means that if you have a claim you will pay nothing towards the costs. We want you to talk to us as soon as there is a problem, and not try and fix it by yourself. So we don't want you to think that you can get it fixed cheaper - you can't!