The entry rate is the percentage of visits starting on a particular page or content area of a website.
The entry rate is calculated as the number of entry page views divided by the total number of visits.
The number is only interesting if it is calculated for a particular page or content areas since it otherwise will amount to 100%.
Notice that if you have more than one websites, a visit could start on another of your websites. If the visit then clicks on a link leading to the website you are analyzing, it will still count as starting here.