How to notify admissions that one quit another program? I completed one term of a master's program before finding it was not what I expected, so I promptly quit. Now, I am sending fall application letters to other master's programs, for which I will be a paying student, but am uncertain how to mention this previous program, or whether that is even necessary. I do intent to send a transcript, as I want to transfer a few credits, however, should I mention this elsewhere in my application? Place a line on my CV? Mention this previous program in my application letters? Offer an explanation upfront describing why I left the program?

I found generally useful advice in Is transferring to another university an option for an unhappy PhD student?, but the answers do not explain what etiquette one should follow in reporting such a situation.
The important thing here is that you realize that you do need to report this information to schools to which you will be applying, as it will matter in their deliberations over your application. That said, you do have some degree of latitude in finding the best way to inform the schools of this. If they have a "special notes" or "additional information" question in the application, that might be a good place to put such information. Otherwise, you would want to mention it somewhere in the cover letter (if you get to include one) or personal statement (if you don't). 

However, this information should be provided by you; don't leave it for the people writing your recommendation letters to mention. That will just raise more red flags.