Explanation:

A number between 100 and 4096. Rules are processed in priority order, with lower numbers processed before higher numbers, because lower numbers have higher priority. Once traffic matches a rule, processing stops.
As a result, any rules that exist with lower priorities (higher numbers) that have the same attributes as rules with higher priorities are not processed. https://docs.microsoft.com/en-us/azure/virtual-network/network- security-groups-overview