Chill hours or units are the total length of time an apple tree needs to be exposed to certain winter temperatures to ensure they flower and set fruit. For more information Heritage Fruit Trees
Espalier is a tree training method that prunes trees flat against a trellis, wire, wall or free-standing.
Laterals are the 10cm and more long growths that grow from below a pruning site and on other parts of the tree. Literally they are shoots that grow sideways from the thicker upright growth.
Multigrafted trees have several different cultivars that have been grafted onto, and growing on the one tree.
Rootstock is the apple tree roots that are selected to graft a new tree on. Particular rootstock can cause trees to be from 20 to 80% shorter than a seedling grown adult tree, depending on the rootstock used. Particular rootstock can also be disease and pest resistant as well as dwarfing.
Spur growth is less then 10cm (some say less than 5cm) that will usually produce flowers and fruit. Once established spurs will fruit for up to the life of a tree.
Stepover is a tree trained to a height of about 50cm. Their diminutive size means they are not very productive, but are ornamental and can be literally stepped over.
Tip-bearing apples have fruit growing on the end of long laterals. Partial tip-bearing apples are those that bear fruit only on the end of some of the long laterals.