Functional (adjective)

1. Designed to be practical and useful, serving a specific purpose or function.
2. Having a practical or useful purpose or function, such as functional furniture.
3. Operating effectively and efficiently, as in a functional system.

Origin:

From latin functionalis, meaning 'of or belonging to a function'.

Examples:

1. The functional kitchen design maximizes storage and work space.
2. The functional lamp provided ample light for reading.
3. The functional car had all the features necessary for a long road trip.
4. The functional website made it easy to navigate and find information.
5. The functional jacket was both stylish and warm.