What is the Costco employee discount?

I'm curious to know more about the Costco employee discount. Can you please explain what it entails? Does it offer a fixed percentage off on all purchases or are there specific categories or items that are excluded? Is the discount applicable only in-store or can it be used for online purchases as well? Are there any eligibility criteria that employees need to meet in order to qualify for this discount? Additionally, does the discount vary based on the employee's position or tenure at Costco? It would be great if you could provide a comprehensive overview of how the Costco employee discount works.