A “long take” is a when a very long shot is used. There are no cuts or interruptions and the camera is continuously filming for a long time. A great example of this is from the movie “A Touch of Evil” (Orson Welles, 1958):

Here, a camera was placed onto a crane in order for it to smoothly travel all the way across the street and dozens of meters more following two characters. It is widely regarded as a masterpiece and one of Welles greatest scenes due to how difficult it would be to get a perfect shot.