What is difference between lan and Ethernet?

LAN stands for Local Area Network. It describes the kind of network you have. It is a data communications network limited to around a 1-km radius.

Because the network is known to cover only a small area, optimisations can be made in the network signal protocols that permit data rates up to 100Mb/s.

Ethernet, on the other hand, refers to the cabling system of the network. It is a way to interconnect computers to form a network. From "Ethernet: The Definitive Guide" by Charles Spurgeon,

Quote:

Metcalfe's first experimental network was called the Alto Aloha Network. In 1973 Metcalfe changed the name to "Ethernet," to make it clear that the system could support any computer-not just Altos-and to point out that his new network mechanisms had evolved well beyond the Aloha system. He chose to base the name on the Word "ether" as a way of describing an essential feature of the system: the physical medium (i.e., a cable) carries bits to all stations, much the same way that the old "luminiferous ether" was once thought to propagate electromagnetic waves through space. Thus, Ethernet was born."

--from "Invention of Ethernet", "Ethernet: The Definitive Guide" by Charles Spurgeon

Ethernet can also mean the physical hardware (the cables). There are many of these: 10Base-T, 10Base-2, 10Base-5, 10Base-F, and the like. There are also faster ones, namely 100BaseT (Fast Ethernet) and 1000BaseT (Gigabit Ethernet).

You can find more info at Charles's Spurgeon's Ethernet (IEEE 802.3) website.