Prospect in Current Organization

This Condition on the Current Org category tab in Search Builder is used internally for some searches that are built on-the-fly. However, you can use it, too.

It will find everyone who is not currently enrolled in the last organization you viewed, but is a Prospect. You can also find Prospects by looking at the Prospect tab of each organization, which is the simplest way to find people that are Prospects.

You would never want to save a search if it contains a Condition that looks at the current org, because that will change each time you log in.