One who makes observations, monitors or takes notice
A crew member on an aircraft who makes observations of enemy positions or aircraft
A person sent as a representative, to a meeting or other function to monitor but not to participate
One who adheres or follows laws, guidelines, etc.
A country or other entity which has limited participation rights within an organization.
A sentry etc. manning an observation post
A viewing window.
A typically rectangular region representing the range or area currently visible (within a window, screen, etc.).
To clip (an image or region) so that it fits in a viewport.