Let’s get some basic definitions down first about SQL Server Security. Take the workplace example where “Tom” needs “Read” access to the “Financial Folder”. What are the Securable, Principal, and Permissions from that last sentence?

A Securable is a resource that someone might want to access (like the Financial Folder).
A Principal is anything that might want to gain access to the securable (like Tom).
A Permission is the level of access a principal has to a securable (like Read).