Definition of "casing"

That which encloses or encases.  examples

(architecture) The decorative trim around a door or window.  examples

(oil industry) A metal pipe used to line the borehole of a well.  examples

(uncountable, computing) The state of letter case across a whole phrase or whole lines of text; the collective state/arrangement of uppercase and lowercase letters.  examples

present participle and gerund of case  examples