This page contain list of TCP Port Numbers
(Dynamic and/or Private Ports) in the range 49152–65535.
It's a last range of tcp ports, thats why it's is empty to 90%, approximately about 1500-2000, some programs using whole range of with range ports.
An easy way to understand ports is to imagine your IP address is a cable box and the ports are the different channels on that cable box, the oldest part of box have is fully reserver becuase it on starting of list.
That host destination may be a different IP using the same port, a different port on the same IP, or completely different combination of the two. Port forwarding is extensively used to keep unwanted traffic off networks.
The port numbers used are often transparent to the end user; the client software will specify the port number. However, sometimes the user can override the defaults.
Port numbers are often used in creating "Firewalls", which provide security on a network. For example, if you didn't want anyone outside of your intranet to be able to access your web server, you could set up a firewall that would prohibit any packet destined to port 80 (the port assigned to your web server) from passing through your routers.
The most well-known from this range:20000 DNP (Distributed Network Protocol), a protocol used in SCADA systems, 27010 Half-Life and its mods, such as Counter-Strike, 36963 Counter Strike 2D multiplayer (2D clone of popular CounterStrike computer game).
In computer networking, the protocols of the Transport Layer of the Internet Protocol Suite, most notably the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP), but also other protocols, use a numerical identifier for the data structures of the endpoints for host-to-host communications. Such an endpoint is known as a port and the identifier is the port number. The Internet Assigned Numbers Authority (IANA) is responsible for maintaining the official assignments of port numbers for specific uses.