The hybrid fir is scientifically named Abies × borisii-regis. It is a natural hybrid between the European Silver fir (Abies alba) and the Greek fir (Abies cephalonica). The epithet borisii-regis was given in honor of Tsar Boris III of Bulgaria.

Hybrid fir is an evergreen coniferous tree belonging to the family Pinaceae. It occurs mainly in the Balkan Peninsula, with a significant presence in Greece. It is typically found in transitional zones between the distributions of its parent species, in mountainous ecosystems with a cool and humid climate.

The tree can reach a height of 25–40 meters, developing a straight trunk and a symmetrical, conical crown. The bark is smooth and greyish brown in young trees, becoming fissured with age. The needles are flat, linear and dark green, arranged in a pattern that helps distinguish the species from its parent forms.

Flowering occurs in spring. The species is monoecious, bearing both male and female cones on the same tree. The female cones are cylindrical and upright during development and mature within the same year, releasing winged seeds.

Hybrid fir prefers deep, fertile, well-drained soils and shows good frost resistance. It requires relatively high atmospheric moisture and does not perform well under dry or hot conditions.

Propagation is mainly by seed. It shows moderate to good growth and is considered resilient under natural conditions, although it has limited tolerance to prolonged drought and high temperatures.

Hybrid fir is primarily used in forestry and reforestation of mountainous areas, and it is an important component of Greek mountain forest ecosystems. It contributes to soil stability, biodiversity conservation and the formation of ecologically balanced forest stands.