What Is a Report?
A report is a saved, named collection of the measures and metrics you want to look at together, arranged in an order you choose. Each report is its own entity with a title, and you manage your reports as a collection.
The phrase "ordered measures and metrics" describes a report's contents exactly: a report holds a list of items, where each item is either a Measure or a Metric, and each item has a display order that determines the order rows appear in. (For the difference between the two, see Metrics vs. Measures.)
A report is reusable across your data. It stores a data-preview configuration — a forecast version, a time grain, and a date range — so you can view the same report against different forecasts and time windows. See Building a Report to create one and Viewing Report Data for how it's displayed.