the state or quality of being well-suited to filling a particular purpose or performing a particular function, or the purpose/function to be filled/performed;
e.g. These shoes are ugly, but I chose them for their functionality, since I can walk very far in them.
(noun)
the set or range of functions or tasks that can be carried out by an electronic system/device or computer software;
e.g. He showed me the functionality of the new computer system in the office.