"Lanceolate" is a term which is used to describe a specific type of leaf shape in plants. A lanceolate leaf is usually around four times as long as the broadest point of the leaf. The tip narrows to a definitive and sharp apex, and the base may be pointed as well, or broad and slightly flared, depending on the species. The shape of the leaf, in other words, resembles that of a lance. This is not to be confused with a hastate or spear-shaped leaf, which has a pointed apex and a bottom which consists of two flared lobes which resemble the base of a spear or arrow-head.
Botanists use very precise terms to describe the shape of leaves as part of a larger library of technical terminology which ensures that descriptions of plants are accurate and uniform. This is very important for plant identification, as it reduces confusion, and it is critical when a botanist is describing a plant which he or she thinks is a new species. Rather than saying "the leaves are kind of long," for example, a botanist can say "the plant has lanceolate leaves," and this provides a wealth of information.
Some other examples of terms in addition to lanceolate used to describe leaf shape include palmate, pinnate, obvate, and lobed. Rhomboid, spatulate, round, falcate, and elliptic are others. Other terms commonly accepted in the lexicon used by botanists to describe leaves include compound, cordate, acicular, and digitate. Some botany guides, especially those which dedicate discussions to leaf shape, have charts depicting different leaf shapes which people can use to learn about the subtle distinctions between types of leaves.
For lay people, there are a number of situations in which it may be helpful to understand what a lanceolate leaf looks like. People who use botanical keys to identify plants they encounter on trips and walks need to be able to distinguish leaf shape because it is often an important element of a key. Gardeners also need to know their leaf shapes, as gardening catalogs often use botanical terms to describe plants, and it helps to be able to visualize the text in a gardening catalog.
Plants have developed differing leaf shapes for a variety of reasons. Certain types of leaves are better for different climates, or the specific survival mechanisms used by a particular plant. Leaf shape can facilitate photosynthesis, affect the intake of nutrients through the leaves, and shade of the base of the plant to prevent sun damage, among many other things.