Only five major cultivated pepper species produce the 50,000 estimated pepper cultivars grown worldwide. The vast number of pepper plants are cultivars, or different breeds of the same species. For example, the common bell pepper (with zero heat) is the exact same species (Capsicum annuum) as the spicy cayenne (30,000-50,000 SHU) and the jalpeno. They're all different cultivars of the same species. It's through the processes of selective breeding and hybridization, that have made them very different from one another in both look and heat level.
Over the last few thousand years, pepper varieties have evolved from plants with simple round, red, berry-like peppers with modest heat to the many varied peppers of today. And, pepper growers everywhere are continuing this process (some unknowingly).
In botany, a scientific naming nomenclature is defined in an attempt to precisely communicate the boundaries between plant populations. For these scientific names, part of the convention is to italicize any Latin components of the name.
As referenced above, using strict terminology, a "variety" should be variation within a species produced solely by natural means. However, the term "variety" is commonly misused to include cultivars. We've noticed this to be especially true when referring to different types of chile peppers. Many online growers do it, Wikipedia does it and even books on chile peppers do it.
Additionally, human cultivation of chile peppers goes so far back, that it'd be difficult to prove a certain pepper "variety" had no human help. The interchanging of variety and cultivar is so pervasive within the chile industry, that we have chosen to use these words interchangeably as well.
The essence of being a cultivar is consistency. A cultivar should consist of plants and fruit that look and taste very similar to each other. If self pollinated, or pollinated by the same cultivar, the seeds should "come true" and produce offspring that are very similar to their parents. It's this consistency that gives us the convenience of planting jalapeno seeds each year and getting the expected result.
How this consistency is achieved is due to a pepper variety (cultivar) being selectively bred to be nearly homozygous – meaning its matching chromosome pairs are nearly identical. And, in instances where the pairs don't match, those genes either don't produce significant, noticeable differences, or any difference-making genes are recessive and rare. Recessive and rare genes are usually paired with dominant genes – effectively hiding those recessive traits, as it's mathematically unlikely a plant seed would get a pair of two rare recessive genes. This results in a cultivar where the pollen chromosome almost always matches the egg chromosome (at least in terms of trait expression) and will consistently produce seeds with very similar genetics.