What is the relationship between Ethernet and LAN?

Ethernet is a communication protocol for Local Area Network.

LAN are independent networks but may be linked.

Ethernet is within your router, and protected by the firewall, LAN is wherever you select and can be outside, wireless or whatever. LAN is the least secure and very hackable.

When you have a program in your computer talking to a program in some other computer, you have a physical connection between your computer and (probably) your in-house router.  The physical connection would be over a cable and might well be an Ethernet cable.

Once your computer connects to the router that runs your in-house network, it can very easily talk to other computers and devices that talk to the same router.  They are ALL physically connected by Ethernet.  The GROUP of things connected that way to the local router is a Local Area Network (LAN).

Therefore, members of the LAN talk to each other using physical Ethernet cables.

Ethernet is a communication protocol for Local Area Network.

LAN are independent networks but may be linked.

Ethernet is a communication protocol for Local Area Network (LAN) using the same media interfaces (mainly RJ45 or fiber). 

LAN are independent networks but may be linked within a WAN through Internet devices such as cable, Routers. 

Ethernet is a communication protocol for Local Area Network (LAN) using same media interfaces (mainly RJ45 or fiber). LAN are independent networks but may be linked within a WAN through Internet devices such as Routers

Ethernet is a Xerox trademark for a particular type of LAN protocol. There are dozens (if not hundreds) of other LAN protocols, including token ring, token bus, FDDI, and predecessors such as AppleTalk, Banyan Vines, etc.

Ethernet is a communication protocol for Local Area Network (LAN) using same media interfaces (mainly RJ45 or fiber). LAN are independent networks but may be linked within a WAN through Internet devices such as Routers

LAN is Local Area Network.  It carries Ethernet.

Ethernet is a standard for connecting many types of network device.

LAN is "Local area network", the part of the internet system that is "inside" your router's firewall and noramly using private IP addresses issued by the router.

The connection from the router to the internet and through your internet providers equipment is WAN - Wide area network, the internet that uses public IP addresses etc.

Ethernet is a commonly used network connection system, but it's not the only one by any means.

There are such as fibre optic systems, "Infiniband", equipment that has SFP sockets for a plug-in choice of interface types, token ring and others.

Those are mostly faster than common ethernet types, but also more expensive and generally the interface cards need a lot more power than an ethernet port as well.