Which category of products does first class mail belong to?

First-class mail is categorized as a service provided by postal systems for sending letters and lightweight packages. This category emphasizes efficiency and speed, allowing for delivery in one to three days, depending on distance. It is distinguished from other categories like courier or express services, which may guarantee faster delivery but often involve different pricing structures and may include additional features, such as tracking or guaranteed delivery times.

First-class mail typically serves personal and business communication needs rather than large shipping logistics associated with services like courier or shipping. Thus, it is accurately classified within the shipping category as it pertains to sending mail and light packages through traditional postal services.