I recently ate a turkey tenderloin at a friend's house. Pre-cooked, it looked like two boneless breasts inverted and packaged together. When grilled, it had a totally different texture from your basic breasts. What is this cut? Is it simply processed bird formed to look similar to pork tenderloins? The package read "Turkey Tenderloin with up to 30% flavoring solution". Can anyone tell me what this is, exactly?

Never heard of that, and the "30% solution" added would scare me away. That's 30% of the cost you're paying for water and very little seasoning. My guess it's a processed cut made up of something else. The small part under the breast (that falls away when you slice) is usually called a tenderloin