Well Know Ports vs Registered Ports
There are two ranges of ports used for TCP/IP networks: Well-known ports and Registered ports.
The well-known ports are the network services that have been assigned a specific port number (as defined by /etc/services). For example, SMTP is assigned port 25, and HTTP is assigned port 80. Servers listen on the network for requests at the well-known ports.
Registered ports are temporary ports, usually used by clients, and will vary each time a service is used. Registered ports are also called ephemeral ports, because they last for only a brief time.The port is then abandoned and can be used by other services.
Well-known Ports range = 1–1023
Registered Port range = 1024–65535
As a rule of thumb, always remember.
Connections to ports number 1023 and below are assumed to run with root-level privileges. This means that un-trusted services should never be configured with a port number below 1024.