When a plane overflies a place, it goes through the sky above that country, city, or stretch of land. It does not land there; it only passes over. The word belongs to news, law, and official talk more than to the kitchen table, because it is really about airspace — the sky a country treats as its own — and who may cross it. You will read that a jet overflew an island, or that airlines were told not to overfly a war zone. Everyday English more often just says fly over. The verb follows fly: overfly, overflew, have overflown. That last form matters: overflown is the plane; overflowed is water, or a list that got too long.