Plant Habit is the form of growth that characterizes a species. It includes the shape of the overall plant and other characteristics, like whether it has woody parts, climbs or stands erect on the ground, grows in a clump and a lot more.
The general appearance of the plant, including size, shape, growth form and orientation.
There's a lot more information about growth habits in this Wikipedia article.
Vascular plant without significant woody tissue above or at the ground. Forbs and herbs may be annual, biennial, or perennial but always lack significant thickening by secondary woody growth and have perennating buds borne at or below the ground surface. In PLANTS, graminoids are excluded but ferns, horsetails, lycopods, and whisk-ferns are included.
Applies to vascular plants only. Federal Geographic Data Committee (FGDC) definition includes graminoids, forbs, and ferns.
Grass or grass-like plant, including grasses (Poaceae), sedges (Cyperaceae), rushes (Juncaceae), arrow-grasses (Juncaginaceae), and quillworts (Isoetes).
Applies to vascular plants only. An herb in the FGDC classification.
Organism generally recognized as a single "plant" that consists of a fungus and an alga or cyanobacterium living in symbiotic association. Often attached to solid objects such as rocks or living or dead wood rather than soil.
Applies to lichens only, which are not true plants.
Nonvascular, terrestrial green plant, including mosses, hornworts, and liverworts. Always herbaceous, often attached to solid objects such as rocks or living or dead wood rather than soil.
Applies to non-vascular plants only; in PLANTS system this is groups HN (Hornworts), LV (Liverworts), and MS (Mosses).
Perennial, multi-stemmed woody plant that is usually less than 4 to 5 meters (13 to 16 feet) in height. Shrubs typically have several stems arising from or near the ground, but may be taller than 5 meters or single-stemmed under certain environmental conditions.
Applies to vascular plants only.
Low-growing shrub usually under 0.5 m (1.5 feet) tall, never exceeding 1 meter (3 feet) tall at maturity.
Applies to vascular plants only. A dwarf-shrub in the FGDC classification.
Perennial, woody plant with a single stem (trunk), normally greater than 4 to 5 meters (13 to 16 feet) in height; under certain environmental conditions, some tree species may develop a multi-stemmed or short growth form (less than 4 meters or 13 feet in height).
Applies to vascular plants only.
Twining/climbing plant with relatively long stems, can be woody or herbaceous.
Applies to vascular plants only. FGDC classification considers woody vines to be shrubs and herbaceous vines to be herbs.
From: USDA Plants Database
Climbing Plants
Climbing plants are also called vines. The stems trail along or coil around other plants or structures as they grow upward. Examples include cucumber (Cucumis sativus), morning glory (Ipomea species), and grape vine (Vitis species). Climbers characterize moist forests and woodlands.
Clump-Forming Plants
Clump-forming or tussocky plants exhibit an aggregate of several shoots growing in a bunch from a common base, especially in grasses. Examples include the bunch grasses Andropogon and Aristida mosses (such as Polytrichum species) and sedges (Carex stricta). They characterize grasslands and are common in the prairies of the United States. They also grow in sandy locations, wetlands, and disturbed habitats.
Dense Plants
Dense plants grow many small, woody canes or stems very close together in an upright fashion. The majority are shrubs. Examples include Ephedra, southern arrow wood (Viburnum dentatum), mountain laurel (Kalmia latifolia), and creosote bush (Larrea tridentata). They characterize woodlands, grasslands, coastal vegetation, and deserts.
Erect Plants
In erect plants, onemain stemgrows in an upright position clearly above ground level. This is common in trees. Examples include banana (Musa), oak (Quercus), pine (Pinus), maple (Acer), and palm. They mainly characterize forests and woodlands and some grasslands.
Mat-Forming Plants
Mat-forming plants have many stolons (creeping stems) that grow in a trail along soil or water surfaces and spread out to produce a matlike cover. Examples include the grasses Cynodon and Digitaria, Kentucky bluegrass (Poa pratensis), crab grass (Digitaria sanguinalis), the aquatic ferns Salvinia and Azolla, andmosses, such as Sphagnum. They characterize grasslands, bogs, wetlands, secondary forest floors, and cultivated habitats.
Mound-Forming Plants
Mound-forming plants grow to form a rounded shape resembling a mound or swollen bump. Examples include the barrel cactus (Ferocactus and Echinocactus), several other species of cacti (such as Gymnocalycium), and Euphorbia gymnocalycioides. They characterize deserts, grasslands, and the tundra.
Open Plants
Upright, woody stems or canes growing in an erect fashion characterize open plants. Their growth resembles a dense habit but has fewer stems and an open, airier structure. Examples include some bamboos (Bambusa), black willow (Salix nigra), smooth alder (Alnus serrulata), and meadowsweet (Spirea). This is characteristic of some shrubs and small trees of forests, woodlands, wetlands, and grasslands.
Prostrate Plants
The stems of prostrate plants grow flat on the soil surface or almost touching (hugging) the ground but not trailing. Examplesinclude the herbaceous milkpurslane weed (Euphorbia supina), common mullein (Verbascum thapsus), and some species of juniper. They are common in the tundra, grasslands, wetlands, and disturbed habitats.
Scandent Plants
Scandent plants have prominent stems in a leaning position. Examples include sugarcane (Saccharumofficinarum), coconut palm (Cocos nucifera), bearberry (Arctostaphylos uva-ursi), blackberry (Rubus fruticosus), and some bamboos (Bambusa). They characterize the dwarfed, woody trees in the timberline of the tundra, savanna, forest undergrowth, and coastal habitats.
Spreading Plants
Spreading plants exhibit a sprawling type of growth, resulting fromprofuse lateral branching in mostly woody or succulent stems. Examples include common juniper (Juniperus communis), blueberries (Vaccinium), prickly-pear cactus (Opuntia), Sumacs (Rhus), and ferns (such as Adiantum). They characterize forest undergrowth, grasslands, sandy coastal areas, deserts, cultivated lands, and some areas of the tundra.
Stemless Plants
Stemless plants have no visible stem above ground and are composed mainly of leaves or leaflike structures. Examples include common dandelion (Taraxacum officinale), Aloe vera, sisal (Agave), onion (Allium cepa), and liverworts (such as Marchantia polymorpha). They characterize aquatic and wetland vegetation, deserts, some grasslands, cultivated land, and wasteland.
An upright, reasonably large [more than (3-4) 5 metres tall] woody plant, usually with a single stem.
An upright (or spreading horizontally and then becoming upright) multiple stemmed woody plant which is generally smaller than a tree (usually less than 5 metres tall).
A woody plant with branches spreading along the ground or lying flat on the ground, or spreading along the ground for most of its length but with tips turning upwards.
Woody or herbaceous plants with stems that are not self-supporting, but are climbing or straggling on some support.
Herbs (or rarely shrubs) with a whorl of leaves (by contraction of stem internodes) at the base of the stem, or non-woody, non-climbing plants.