A granted or issued US patent is an actual patent. It can be enforced in court if someone infringes — or trespasses — on the claims of the patent. The claims are the section of the patent which defines the patent right that has been given. Before your patent is granted, you have a patent pending.
A US patent application is a request to obtain a patent. US patent applications are usually published 18 months after the initial filing date.
The claims in a patent application may change after publication, and in fact, usually, do. This is because the US patent examiner will compare the claims to the prior art, and may require the applicant to change the claims in order to obtain a granted patent. The prior art is everything published before the initial filing date of the patent, everywhere in the world, and in every language.
Sometimes US patent applications become abandoned before they are granted. This can happen for many reasons. For example, the examiner may find prior art that shows that the invention in the patent application isn’t new (novel) or is too similar to the prior art (obvious).
