Hybrid fruit varieties arising from crosses between fruits of different species.
New fruit varieties are usually developed by crossing varieties of the same species. However new varieties can also arise from inter-breeding between varieties of different (but related) species. These are known as hybrid or inter-specific varieties.
Hybridisation is particularly common in stone fruits such as plums, cherries, and apricots. Indeed the common plum (Prunus domestica) is thought to be natural hybrid between a sloe (Prunus spinosa) and a cherry-plum (Prunus cerasifera). Although these days most hybrids are developed in university-led research programmes, they are not genetically modified (GMOs) - the process is still based on taking pollen from one variety and pollinating another in the hope of producing a new variety with the desired mix of characteristics.
Apricots are a particular focus in the development of new inter-specific fruit varieties because they naturally produce larger fruits than cherries or plums, and will easily cross-pollinate with them.