Displayed IP address is address, that is asigned to your device (computer, smartphone, router or another device). Web server can identify your device by this IP address.
IP address (Internet Protocol Address) is a numerical label of device connecting to computer network that uses the Internet Protocol, e.g. Internet Protocol Version 4 (IPv4) or newer Internet Protocol Version 6 (IPv6).
Internet protocol suite contains e.g. DHCP, DNS, FTP, HTTP, IMAP, NNTP, NTP, POP, SMTP, SNMP SSH, Telnet, TLS/SSL and more in the application layer, transport layer (TCP, UDP, RSVP, ...) and internet layer (IP, IPv4, IPv6, IPsec, ICMP, ...).
TCP/IP is the acronym of Transmission Control Protocol / Internet protocol.
Devices connected to computer network include physical address known as MAC address. MAC i acronym of Media Access Control. MAC is a unique identifier asigned to a network adapter by the manufacturer. MAC is using for identification. Another names for MAC are: EHA - Ethernet Hardware Address, hardware address or adapter address. Desktop computer, notebook or smart phone may have more than one MAC address (e.g. one for wireless adapter and one for ethernet port).
In Windows XP, Vista, 7 and if you have TCP/IP installed you can see IP and MAC addresses of all network adapters in CMD. Run CMD and enter ipconfig /all
In Windows 95, 98, ME and if you have TCP/IP installed you can see IP and MAC addresses of all network adapters in winipcfg application. Click Start then Run and type winipcfg and click OK.
In Mac OS X up to Tiger and Mac OS X 10.4 you can see IP and MAC addresses of all network adapters in Apple menu then select System Preferences then select Network.
For example in Ubuntu: IP address and MAC address is shown in Connection Information. Right click the network icon (two vertical arrows pointing up and down) in your notifications area.
Method 2: Enter command ip addr show in Terminal. This return information of each ethernet connected device.