An IP (Internet Protocol) address is a unique numerical representation of a computer on a network. Every computer connected to the Internet is identified by an IP Address. Usually, IP addresses are dynamically assigned to a computer by a dedicated server called DHCP Server (Dynamic Host Control Protocol), and hence change from time to time as and when the connection is lost and reestablished.
However, there are scenarios where a static IP address is more preferable, e.g., in large corporations, where it removes the load of using DHCP for each computer in the organization.