Most public roadmaps are marketing documents with a Gantt chart attached. This one is a status list with four states and no dates, because dates on a roadmap are a promise we would break.
Shipped is in production and you can use it today. Building now has a settled specification and engineers on it. Up next is committed for the current quarter but has not started. Exploring means we believe the problem is real and we have not decided how or whether to solve it.
The detail thins out as you move down the page. That is deliberate. We know a great deal about what we are building this week and very little about what we will build in nine months, and writing the second one at the same level of confidence as the first would be dishonest.