FTers often talked about codeshared flights, exactly what does codeshare really mean? I often noticed that UA codeshares with partner airlines. For the same itineraries, they almost always cost more to purchase codeshared tickets with UA than to purchase tickets with partner airlines. Do you not receive EQM or EQS from other partner airlines if buying direct?

That's when one airline tag their flight # on a partner's flight. In most cases you'll get full flight miles but not the bonus miles offered in some elite programs, best to check out the FAQ.

You get bonus miles offered whether you purchase tickets under codeshare or not. These rules are shown in MP+ programs. They all depend on your ticketing class.

If one buys code-share UA flight, but actual flight is operated by OZ (for example), (s)he does not earn bonus miles.

Right, and similarly if it's an OZ codeshare on UA metal you do get the bonus. All that matter is the metal the flight is flown on in that regard.

It's also possible to have codeshares on airlines that don't earn any miles on UA at all. Sometimes a codeshare is sold just to make it look like UA can get you all the way to somewhere they don't actually fly. Not sure if they have any currently, but it's possible.

Codeshares have absolutely nothing to do with earning miles. If Air New Zealand operates the flight and you've given them your UA MP#, you're going to earn the miles that UA gets for NZ flights. Regardless of whether that NZ flight has a NZ code, a UA code, a Thai code, a Lufthansa code or whatever. It'll be based on what the operating airline (the "metal" around here) has in their own reservation system for it for that booking class and what that NZ booking class earns in United Mileage Plus.

Which by the way is different from how AA AAdvantage works over in oneworld, where codeshares do matter. In Star Alliance programs it's always the metal and the operating carrier's "real" booking class that matters.

Not always true that the codeshare costs less. In some cases, US codeshares on UA metal are less than the same UA flights. Mix of LH codes on UA metal one direction and UA own code on return often price out cheaper than all-UA on the same flights on TATL, due to oddities with how LH and UA do the surcharges differently.

With the exception of CA.

I've always thought it was kind of funny that United technically considers TED flights as codeshare flights

How so? (not that it's funny, but that UA considers them codeshares)

All TED flights have the 'Star Alliance/Code Share/United Express' symbol next to them in the timetable:

http://www.uatimetable.com/United.pd...+timetable+PDF

Although it could have something to do with the even more confusing "Operated by: United for Ted" listed when you book a flight. RAR!

Why is that confusing? The flights are operated by UA. The flights are marketed by TED. That's the textbook definition of a codeshare.

The first time I ever heard the phrase, I mis-heard it as "co-chair", and immediately saw a mental image of two pilots up front, one from each airline...

Oh great, just when I thought I finally understood this.
I guess you mean the second part of this sentence:

What's confusing, other than that Ted is UA anyhow, is that for other codeshares, the "for United" is not part of it.

"UA2345 operated by US Airways". NOT "UA2345 operated by US Airways for United"

The TED codeshare verbiage is just awkward because it's really saying UA operated by UA for a make-believe different brand of UA.

Yes. Luckily, that's the only exception I know of at this point.