A denailer is a tool

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

 for removing nails from lumber

Lumber

Lumber or timber is wood in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production....

 to facilitate its reuse.
Two types of denailer are available.

Portable

A portable denailer is a hand-held pneumatically-powered

Pneumatics

Pneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...

 tool.
It works by driving out the nail from the point end in pieces of nailed lumber which have been pried apart. The process of denailing (removing large numbers of nails from salvaged lumber) is greatly expedited by using this specialized tool.

Stationary

A stationary denailer is a machine designed for single-purpose use,
e.g. pallet

Pallet

A pallet , sometimes called a skid, is a flat transport structure that supports goods in a stable fashion while being lifted by a forklift, pallet jack, front loader or other jacking device. A pallet is the structural foundation of a unit load which allows handling and storage efficiencies...

refurbishing.