A more thorough explanation:

Patent-term extension is a process of extending the time period for which a patent remains valid. This extension is given to inventors to compensate for the time lost due to administrative delays such as interferences, secrecy orders, or appeals.

The extension applies to utility and plant patents issued after June 7, 1995, and before May 29, 2000. The maximum length of the extension is five years.

Suppose an inventor filed a patent application in 1996, and the patent was granted in 1999. However, due to administrative delays, the patent was not issued until 2001. In this case, the inventor can apply for a patent-term extension of up to five years to compensate for the time lost due to administrative delays.

Another example could be an inventor who filed a patent application in 1998, and the patent was granted in 2001. However, the inventor faced an interference proceeding that delayed the issuance of the patent until 2003. In this case, the inventor can apply for a patent-term extension of up to five years to compensate for the time lost due to the interference proceeding.

These examples illustrate how patent-term extension works and how it can benefit inventors who face administrative delays in the patent issuance process.