What are “concurrent” visitors?

Concurrent visitors are the total number of people simultaneously on your site at any one moment in time.

What is a “seat”?

A seat is an individual license to a personalized newsbeat dashboard and account. Seats give you complete flexibility over who sees what, so everyone is focused on what’s important to them. Each of the newsbeat plans comes with a preset number of seats, but you can add seats at any time.

via Web Analytics Plans & Pricing: Newsbeat Monitoring Plans for Publishers.