In fixed-wing aircraft category, a gunship is an aircraft having laterally-mounted heavy armaments (i.e. firing to the side) to attack ground or sea targets. Most often, a gunship attacks the target while circling over it, performing a constant pylon turn. This is in contrast to a standard attack aircraft equipped with forward-firing weapon, that flies at the target and then passes over it.
The rotary-wing aircraft (helicopters) can use a variety of combat maneuvers to approach target. In their case, the term gunship is synonymous with heavily armed helicopter. Specifically, dedicated attack helicopters also fit this meaning. In any of these cases, the gunship armaments include machine guns, autocannon, missiles, etc.