Well, that's what the documentation says.
In reality it is a really versatile Port Scanning Tool and has a multitude of uses.
I use it to test my own LAN/WAN and to make sure that my port of Snort (a network intrusion detection system) is working ok. It will set off Snort alarms which is good, but if you are scanning someone be careful. You can set a flag to send off a false client address. (meaning YOUR address) read the documentation for that one. The flag is usually -D123.123.123.123 where 123.123.123.123 is a false TCP/IP address but you can also enter in -Dwww.microsoft.com if you want :)
In some countries this tool may be considered illegal so you might want to hide your address using the above method.

Installation Instructions
Run the installation package. The html documents and readme will be in /boot/home/nmap and the executable /boot/home/config/bin so you can execute it anywhere.

The most common way to run it is:
nmap -v -sS -O -p 1-80 123.123.123.123
where:

• -v is verbose mode
• -sS is TCP SYN stealth port scan (best all-around TCP scan)
• -O is Use TCP/IP fingerprinting to guess remote operating system
• -p 1-80 is what ports to scan(in this example 1 to 80). If omitted, all ports are scanned as defined in one of the 3 files mentioned below.
• 123.123.123.123 is the tcp/ip address to scan

There are 3 files which reside in /boot/home/config/share/nmap

• nmap-os-fingerprints
• nmap-rpc
• nmap-services