Which of the following best describes a Vertical Takeoff and Landing (VTOL) aircraft?

A Vertical Takeoff and Landing (VTOL) aircraft is defined primarily by its ability to take off and land vertically, which distinguishes it from traditional aircraft that require a runway for these maneuvers. This capability allows VTOL aircraft to operate in confined spaces and urban environments where traditional runway access may be limited or unavailable.

The design of VTOL aircraft enables them to ascend and descend vertically like a helicopter but may also possess horizontal flight capabilities similar to those of fixed-wing aircraft. Their versatility in operation makes them suitable for a variety of missions, including urban air mobility and military applications.

The other options do not accurately describe the features of a VTOL aircraft. For instance, the assertion that VTOL aircraft can only fly in one direction or that they require long runways is incorrect, as they can operate in multiple flight modes. Additionally, the requirement for a pilot on board is not a defining characteristic of VTOL aircraft, as some models can be designed for remote or autonomous operation. Therefore, the definition centered around their capability to take off and land vertically encapsulates the essence of what defines VTOL aircraft.