Code Share: what does it mean?
 

Several posters have warned about Code Share.
What is it?
How do I know if my carrier selection is a code share?

codeshare means the airline is using another airline for part of your trip. on the delta website there is an asterisk by any leg of the flight that is serviced by a codeshare partner. then you click on the flight number (i think) and you can view which airline is being used. i don't know if orbitz and the like show who the codeshare partner is. i think the airlines mite be required to show that info on their own websites.

I don't think that codeshare is a neccesarily bad thing or something to be avoided. Because United has codesharing with Luthsansa I will be able to fly all the way to Rome from the west coast with a UAL ticket even though only the first leg is UAL.

It's easy to notice whether a flight is codeshare or not. If the flight numbers are in the thousands (over 2,000) or so, you should investigate further. [The 2,xxx and 3,xxx are usually commuter flights, and the even higher ones are usually code-share.]

For example, AA6119 from LAX to HKG is clearly not an AA flight. Instead, you're flying on a Cathay Pacific plane.

How an airline designates which of its flights are operated by codeshare partners is not uniform so the previous post about numbers being in the thousands may or may not be pertinent to the particular airline(s) you are interested in.
Codeshares are a convenience as much, if not more so, for the airlines themselves in terms of ticketing procedures.
In terms of there having been a "warning" about codeshares, I suspect it had to do with making sure you realize that your flight segments may be operated by another (the codesharing) airline rather than the airline you paid the money to for the ticket. A codeshare situation may also mean that you check in at the OPERATING airline's counter rather than the airline to whichj you paid your ticket money.