A cultivated variety: a breed of plant that is created or sustained by human activity, by propagation. In the case of apples, which do not breed true from seed, all such propagation is by grafting.
The reciprocal of apple cultivar, more or less, is the pippin, an apple variety grown from seed. In a sense all cultivars began as pippins. Those not preserved through cultivation become extinct at the death of the ungrafted tree.
Modern apple-breeding programs routinely destroy thousands of varieties for every new apple brought to cultivation. Arguably these rejects are cultivars too, though a short-lived. (If so, were they never pippins? Discuss.)
Cultivar and pippin describe a relationship between apples and human society, fittingly for a fruit that would be fundamentally different without human selection and care. These terms say something about the fruit, but also about us.
The International Code of Nomenclature for Cultivated Plants formally denominates cultivars by placing the cultivar name, in single quotes, following the traditional Linnean name, for instance, "Malus domestica 'Granny Smith'." The single-quote name is called an epithet.
The International Society for Horticultural Science describes the rules for names and epithets. Some of these rules might arguably disqualify some apple names, for example Honeycrisp under Art. 21.24, exaggeration. (Oh, probably not though.)
Some older cultivars include the word "Pippin" as part of their name, creating a taxonomic paradox. It probably seemed like a good idea at the time.