How would you explain this in an interview? What is Ethernet?

Ethernet is a common packet transmission methodology that allows for collisions and retransmission. It is provides excellent quality results (even with inevitable retransmissions) and can be adapted to very high speeds.

(You could add that it contrasts with Token Ring and other older packet transmission methodologies).

I would go short and snappy

"Ethernet is a standardised family of computer networking technologies used to connect computer systems into a network"

But then I am a software guy and would not be applying for a networking position.

Ethernet is a networking standard created and patented by Intel and Xerox.  The most important part is the formatting of the data into packets that can be recognized and can carry higher level data formats like TCP/IP, the standard that is used on the internet and most LANs these days.  

There are several hardware standards used with Ethernet including the common cables with RJ45 connectors and 4-pair cables.  There used to be at least two different systems using coax cable.  The first was RG6 which was a fairly large cable and the other used RG58, a smaller cable, and was called 'Thin Ethernet'.

Ethernet is VERY different from Token Ring (IBM) and the interviewer may wish to know.

Anybody that used "Ethernet" and "packet" in the same sentence wouldn't get the job if I was doing the interview.  :-D

Ethernet = frames this is true, L3 = packets.  

Seriously, just take your time, I'm not looking for the first person who answered but the best answer.

Cheers and thanks all.

R

Since most job interviews ask questions that should be answered in a short concise fashion I would say something like:

Ethernet is a method used for connecting multiple devices together to form a local area network (LAN) through the use of cables. The most common cable uses an RJ45 connection which appears much like a standard RJ11 telephone connector only slightly larger.

It really depends on the interviewers level of knowledge and what the position the interview is for. The above may not be sufficient for a network technician. They may want more information such as the three currently used speeds such as 10, 100 and 1000Mbps. They may also want to know that you are familiar with the various types of cables, however I would expect to ask those as follow-up questions to the initial question you have asked.

I am a Network Manager and this is what I would like to see IMHO

@pony10us makes a good point. What job are you applying for and who are you meeting with?

A highly detailed answer when applying for a Web Developer role says to the interviewer that this might not be right role for you and the same answer to a HR person could be far too technical and make you look like you are either trying too hard or do not have the people skills to tailor your message to the audience.

I have been applying for a senior network engineer position with a Cisco background.

Thanks Don Johnston and I agree with your changes.