In the following figure, what does the line LCP closed mean?

The LCP closed line states that the LCP process has not completed. This could be due to numerous reasons, such as conflicting options or authentication failure. When the LCP process has completed, it will be in an "open" state when reviewing the interface. The router does not need to have an IP address configured since this is a layer 2 communication process. If the serial line was disconnected, the interface would show as down with a line protocol of down.