An SharePoint Portal Server Listing is like a link with lots of meta data.
When clicked, it can take the user to a URL or to some rich text. It can
have an associated image, be set to expire, assigned to an audience, be
grouped, shown in multiple areas, etc. There are several specialized Web
Parts for displaying the List of Listings for an Area.

Although not specified as such, News in SharePoint Portal Server is also a
type of Listing.

I haven't found a way to distinguish a listing
as a News item or just a regular listing. Can you elaborate on that?

Most areas have a list of Listings provisioned for you. The News Area has a
list of News provisioned for you. Look at the differences when you create a
listing in a non-News area and when you create a News entry in a News Area.
They are identical except in name.

I speculate that Microsoft is just using Listings to implement News. That's
all.

I didn't mean that you could choose whether a listing  was News or not. Sorry
if that was confusing.