“Heirloom” tomatoes and other vegs - it refers to the older varieties. The ones that are not genetically fiddled with. The reason some prefer to grow heirlooms are because you can harvest and store the seeds, and the produce does tend to have better flavor. Heirloom seeds will grow a true variant of the parent plant.
The more common seeds, non-heirloom types, that one tends to find in most retail stores, will only produce for that one season they are planted. If you were to save and plant seeds from those, you will not get the same quality/variety of the plant the seed was harvested from. Actually many seeds won’t (re)produce at all.
Bottom line is that most heirloom vegetables have more and better flavor. I choose to grow heirlooms because of the taste factor, with the bonus that we can save the seeds - never have to buy seeds more than the initial layout. Win-win.
(I wonder what an heirloom turkey is though)