Field of view is the angular extent of a scene a lens and sensor combination actually captures, usually measured in degrees horizontally, vertically or diagonally.
Field of view is the actual angular slice of a scene a given lens and sensor capture, usually quoted in degrees, and it is the checkable fact behind a vague hope that a lens will be wide enough. Focal length alone does not tell you this, because the same lens covers a different angle on each sensor size. Knowing the real number lets a photographer confirm a shot will fit before travelling to the location.
Photographing a 20-metre building facade from a courtyard only 15 metres deep, a 35mm lens on full frame covers about 54 degrees horizontally, which is not enough, while a 20mm at about 84 degrees just takes it in. Field of view also drops off faster than people expect as focal length climbs, so the jump from 24mm to 35mm loses far more of the scene than the small number change suggests. Checking the horizontal angle against a room's dimensions beats turning up with two lenses and hoping one works.
A real-estate photographer needs to show a full bedroom in one frame from the doorway, standing about 4 metres from the far wall, which is roughly 4 metres wide. A 24mm lens on full frame gives about 74 degrees horizontally, which at 4 metres covers a width of around 6 metres, comfortably fitting the wall with room to spare.
A 35mm lens drops to 54 degrees and about 4 metres of coverage at that distance, so the shot only just includes the wall and any furniture in the corners is clipped. Going to a 16mm ultra-wide gives 97 degrees and nearly 9 metres of width, enough for the whole room but with visible stretching of objects near the frame edges, which is why 20 to 24mm is the usual compromise for interiors.