What does "extension" mean?

Additional senses

1. 2.(Logic & Metaph.) Capacity of a concept or general term to include a greater or smaller number of objects; -- correlative of intension. The law is that the intension of our knowledge is in the inverse ratio of its extension. Sir W. Hamilton. The extension of [the term] plant is greater than that of geranium, because it includes more objects. Abp. Thomson.
2. 3.(Surg.) The operation of stretching a broken bone so as to bring the fragments into the same straight line.
3. 4.(Physiol.) The straightening of a limb, in distinction from flexion.
4. 5.(Com.) A written engagement on the part of a creditor, allowing a debtor further time to pay a debt. Counter extension. (Surg.) See under Counter. -- Extension table, a table so constructed as to be readily extended or contracted in length.