Heirloom, Just Old, or Ugly
Heirloom tomatoes are officially a thing! Or so I'm told.
All jokes aside, heirloom tomatoes more than a thing, they're an awesome thing! Since their advent into the marketplace, many other things have been anointed as "heirloom" as the term has come to be synonymous with a level of quality. But what does the word mean and how is it used? How is the term abused? Let's (blanch, and) peel back some tomato skin and learn more!
When a clock or a quilt is a family heirloom, it's an item that's been handed down in the family for generations. While there's no consensus definition of heirloom as applied to tomatoes, this first premise is required in any definition of heirloom - it must be a tomato that's been handed down for generations. When you hand down Grandfather's watch to a new generation, it's as simple as keeping it somewhere safe until you entrust a younger family member to keep it somewhere safe. To pass along an heirloom tomato, you need to save seeds and use those seeds to grow a new crop of tomatoes of the same variety (ideally) every year. Therefore, a hybridized tomato, whose seeds are infertile and designed such that their seeds must be purchased every year and not saved from the fruit, cannot be an heirloom.
Without any real numbers to back me up, hybridized tomatoes (red slicers in the grocery store and their ilk) make up the overwhelming majority of the marketplace but represent a very tiny percentage of the biodiversity of the tomato (tomatoes originated in Mexico, for the nutritional anthropologists out there). It's impossible to quantify the number of heirloom tomato varieties they are because many are open pollinated and the genetic makeup of each tomato can change from year to year. In this way, a seed saver's tomato patch is similar to a livestock operation - such that your neighbor's Green Zebra tomatoes might possess different characteristics than yours if you're selecting your seeds for different quantities.
For me, that's the whole of my definition. While the tomatoes your family brought over from Italy and have grown every year in your garden are, maybe, more heirloom (if there can be such a thing) than my Arkansas Traveler, if the tomato can be passed down (and has been), it's an heirloom in my eyes.
The Arkansas Traveler (pictured above) was an intentional example, to demonstrate a counter argument. One of the first things you'll learn when you study heirloom tomatoes is there are multiple and conflicting stories around the origin of each variety. Many of these are fictionalized and romanticized to make them more appealing. So, depending on which story you believe, the Arkansas Traveler was either passed down "through folks in the Mountains of Arkansas where it was a hillbilly favorite" or it was developed by tomato breeders at the University of Arkansas anywhere from the 1930's to the 1970's. But this much is for sure, the seeds saved from our Arkansas Traveler tomatoes will yield tomatoes similar to its predecessors. Since this has occurred over at least one generation, I consider these heirloom tomatoes. Again, the main distinction being it's viability from seed.
So, why do heirloom tomatoes taste so much better? First, a reminder that language is what we make it to be, just like a wiki. Sometimes, our population gets it right. Sometimes, we abuse terms like "artisan" (NSFW language). But, there's nothing about "heirloom" that automatically means delicious! More than likely, the heirloom tomato seeds were saved by folks because somebody found them tasty. However, I've had plenty of heirloom tomatoes that didn't taste good and a very select few hybrid tomatoes that did taste very good as well. However, by in large, tomato breeders bred hybrid tomatoes to look good, store well, and take abuse. Heirloom tomato seed savers have selected and saved seeds almost exclusively for taste and flavor. And that's why heirloom tomatoes taste better. It isn't that they automatically taste better, it's because they were selected for taste rather than anything but, in the case of their hybrid counterparts.
So! To review, in a very logic problem kind of way. All non-hybridized seeds can be heirlooms, but not every one is. All heirlooms are non-hybridized. Not all "old" tomato varieties are heirlooms, BUT (again) all heirlooms are (at least a few generations) old. Heirloom tomato seeds can be saved based on any preferable characteristic but are most commonly saved because of their superior flavor, often resulting oddly colored and oddly shaped tomatoes that taste good! However, not all heirloom tomatoes are oddly colored and oddly shaped just as not all hybrid tomatoes are uniformly colored and shaped. Anything can be considered "heirloom" if it has been passed down over a number of years, but that doesn't mean it has the characteristics you want.
And that is as comprehensive a lecture on heirloom tomatoes as you'd ever care to read!