At times we come across terms (related to orchids) which are difficult to understand. So I have put together a list of terms which are used when referring to the structure of orchids. This is not an exhaustive list, however I have tried to include more commonly used terms.

Abaxial: the side away from the axis (stem), generally refer to the lower surface
Acuminate: tapering to a slender point
Adaxial: the side facing the axis (stem), generally refer to the upper surface
Adnate: when an organ is joined with another (e.g. a petal attached to the column)
Adventitious: organs which develop at other than usual location, e.g. roots developing from leaves or stems.
Aerial: growing in an exposed condition in air/atmosphere
Anther: part of stamen that produces pollen
Apex: tip
Apical: at the apex of any structure, e.g. at the top of the stem or pseudobulb
Autotrophic: plants which are able produce their own food in the presence of sunlight
Axil: angle formed by a leaf/bract with the axis branch/stem from which it arises
Basal: situated at the base of an organ such as stem or pseudobulb
Bilobate: having two lobes
Blotch: irregularly coloured patch
Bracts: leaf-like organ bearing flower/inflorescence in its axil
Caducous: that which falls off early
Calceolate: slipper-shaped (e.g. flower of a Paphiopedilum)
Capsule: fruit or seed case of orchids
Cauline: growing on the stem
Cilia: minute hair like structures usually found around the margins of organs
Column: reproductive part of the flower, present in the centre and consists of fused male (style) and female (stigma) reproductive organs
Conduplicate: folded lengthwise such that both side are face to face
Connivent: converging but not fused
Corolla: white/coloured inner whorl of the flower, also called the petals
Cymbiform: having boat shaped concave surface
Dentate: with outward facing acute teeth along the margin
Dichotomous: dividing into two, e.g. stem dividing into two branches
Disc: upper surface of the middle portion of the lip
Dorsal: related to the back of a structure like lower surface of a leaf; abaxial
Floral bract: bract from whose axil the flower arises
Foliaceous: having leaf-like appearance
Fringed: hair like appendages present at the margin
Glandular: possessing glands
Gynostemium: column of an orchid flower; the androecium and gynaecium combined
Hyaline: that which is colourless/translucent
Hypochile: lower section of jointed labellum of some orchids
Imbricate: a regularly overlapping surface
Inferior: when describing the ovary which lies beneath the perianth
Inverted: turned upside down; reverse position
Involute: inwardly curved
Labellum: the third petal of orchid flowers, usually enlarged and highly modified
Lamella: a thin flat membrane, scale or septum
Lamina: a flattened part of an organ, like leaf blade, or the broad middle part of the labellum
Lateral: at the side; as in the two lateral sepals of orchid flower
Lip: a modified abaxial petal; the labellum
Membranaceous: thin, more or less translucent layer
Node: joint on the stem from where the leaves or flowers arise
Ovary: part of the flower which contains the ovules, it is present within the flower near its base
Panicle: inflorescence which is further branched, e.g. the inflorescence of Oncidium sphacelatum
Perianth: when referring to calyx and corolla jointly
Petal: part of corolla (flower)
Petiole: narrow stem-like stalk of a leaf
Pollinia: compact mass of pollen found inside the anther
Pseudobulb: swollen part of a stem, occurring in the base, generally found in epiphytic orchids
Resupinate: when an orchid flower twisted by 108 degrees during development such that the lip comes to lie at the bottom of the flower
Rhizome: modified stem which bears roots, may or may not be subterranean
Scape: stem like structure which bears flowers
Tepals: used for perianth when calyx and corolla are similar
Sepal: individual part of calyx, outer whorls of perianth
Velamen: outer tissue on aerial roots of orchids, having sponge-like nature
Zygomorphic: a structure which can be divided into two similar parts vertically, usually used for flowers