Vanilla essence comes in two forms: the actual extract of the seedpods, and the far cheaper synthetic essence, basically consisting of a solution of synthetic vanillin (4-hydroxy-3-methoxybenzaldehyde):
One major use of vanilla is in flavouring ice cream: the commonest, and thus "default", flavour of ice cream is vanilla. By analogy, the term is used, often as "plain vanilla", in computing for default set up of a system, with no extras or modifications.
The species of Orchid that is harvested for vanillin (there are in fact several) is mainly Vanilla planifolia. Most of this genus of one hundred and ten species of vine-like plants have quite large and attractive flowers of green or cream, mostly with a sweet scent. Their leaves are thick and leathery, even fleshy in some species, though there are a significant number of species that have become nearly or totally leafless and appear to use their green climbing stems for photosynthesis.
Below are a few representative species of the genus: