n. The act of extending or the condition of being extended.n. The amount, degree, or range to which something extends or can extend: The wire has an extension of 50 feet. n. The act of straightening or extending a limb.n. The position assumed by an extended limb.n. Medicine The application of traction to a fractured or dislocated limb to restore the normal position.n. An addition that increases the area, influence, operation, or contents of something: an extension for the vacuum cleaner; built a new extension onto the hospital wing. n. An additional telephone connected to a main line.n. An allowance of extra time, as for the repayment of a debt.n. The period of this extra time: three months' extension on the loan. n. The property of an object by which it occupies space.n. A program in a university, college, or school that offers instruction, as by television or correspondence, to persons unable to attend at the usual time or in the usual place.n. Logic The class of objects designated by a specific term or concept; denotation.n. Mathematics A set that includes a given and similar set as a subset.n. Computer Science A set of characters that follow a filename and are separated from it by a period, used to identify the kind of file: In most operating systems, file names having the extension .EXE are executable files.