What does casing mean?
A casing is an outer layer or shell that encloses, protects, or frames something else. The word appears across many domains: the metal or plastic casing of a smartphone, laptop, or engine; the wooden casing that trims a doorway or window; the natural or synthetic casing that holds sausage meat together; and, in oil and water-well drilling, the steel pipe lining a borehole to stop it collapsing. Because it describes function rather than form, casing pairs readily with materials — aluminium casing, rubber casing, outer casing — making it a versatile term in both technical manuals and everyday speech. Connotations are practical and neutral: a casing is typically something sturdy, functional, and slightly secondary to what it protects. The word derives from 'case', ultimately from Latin 'capsa', meaning a box or container, and its ubiquity reflects how often we think of objects in terms of their coverings as much as their contents.
An outer protective covering or housing enclosing a device, machine, or structure.
"The drill bit cut cleanly through the aluminium casing."
Common in technical and engineering contexts.
The moulding or framework surrounding a door or window opening.
"She painted the white casings a soft sage green to match the shutters."
In British English this is more often called an architrave.
A skin or sheath, especially one enclosing sausage meat.
"The butcher stuffed the mixture into natural hog casings."
A lining of steel pipe inserted into a drilled well or borehole to prevent it collapsing.
"The crew lowered the first string of casing into the wellbore before cementing it in place."
Primarily used in petroleum and water-well drilling industries.
Standard plural; countable in all senses.
"All three casings had cracked after years of exposure to sunlight."
The word 'casing' once helped burglars describe 'casing a joint' — sizing up a building before a break-in — long before it described your phone's protective shell.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of casing
Casing derives from the noun 'case', which entered English via Old French from Latin 'capsa', meaning a box or container. The suffix '-ing' formed a noun denoting the material or action associated with the base word, so a casing is literally 'that which cases' — the thing that encloses. Cognates sharing the Latin root include 'capsule', through late Latin 'capsula', a diminutive of 'capsa', and 'chassis', borrowed via French from Latin 'capax'. The word has been used in English since at least the early modern period, with senses expanding alongside technology into machinery, construction, and drilling.
Related word forms
How casing is actually used
Register is neutral; 'casing' appears freely in both technical writing (engineering, construction, drilling) and everyday speech. In American English, 'casing' specifically denotes the trim moulding framing a door or window, a sense more often called 'architrave' in British English. The slang sense 'to case a place' derives from the verb 'to case' rather than this noun.
Easily confused with casing
A caisson is a watertight structure used in underwater construction, whereas a casing is any general protective covering or shell around an object.
Casting refers to an object made by pouring molten material into a mould, while casing refers to a cover or enclosure placed around something.