Power windows: It activates the internal mechanism that rolls the windows up and down.
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It may be manually activated with a window crank, or electrically activated with just a switch. Cranks are always attached to the door itself, while switches may be either on the door or the central console.
About 3 yrs ago I had the same exact issue. Found a reddit thread, open the back door, while pressing the window open button and slam the door. It free up the window, lubricated the window track. Never had problem again