espalier

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A tree or shrub that is trained to grow in a flat plane against a wall or trellis, often in a symmetrical pattern.
• noun A trellis or other framework on which an espalier is grown.
• transitive verb To train as or on an espalier.
• transitive verb To provide with an espalier.

from The Century Dictionary.

• noun In horticulture: A trelliswork of various forms on which the branches of fruit-trees or -bushes are extended horizontally, in fan shape, etc., in a single plane, with the object of securing for the plant a freer circulation of air as well as better exposure to the sun.
• noun A tree or plant trained on such a trellis or system. Trees trained as espaliers are not subjected to such abrupt variations of temperature as wall-trees.
• To train on or protect by an espalier, as a tree or trees.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Hort.) A railing or trellis upon which fruit trees or shrubs are trained, as upon a wall; a tree or row of trees so trained.
• transitive verb To form an espalier of, or to protect by an espalier.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A latticework used to shape or train the branches of a tree or shrub into a two-dimensional ornamental or useful design, as along a wall or fence.
• noun A plant that has been shaped in this manner.
• verb To train a plant in this manner.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a trellis on which ornamental shrub or fruit tree is trained to grow flat