Tickets are the total number of entries across all your Magic events in a rolling calendar year. All play counts.
Tickets count the same player multiple times. A player drafts at 6PM on Friday, that's a ticket. They come back for the 9PM, that's another.
For example, if a player participates in all four of your Prereleases and two of your Friday Night Magics events in a year, that's an Engaged Player.
Events have a calendar life of one year. After that year, they will rotate out, and the new events you run will help replenish them.
Both Tickets and Engaged Players help determine how many Promo Packs your store will receive for the season.
Activated Players are players that join six events in their first year of in-store play. They are very similar to Engaged Players, but the events they join can be any format.
You'll see your Activated Player total in the weekly WPN Update, although it's only relevant if you're interested in pursuing WPN Premium.