Binocular field of view as the name suggests is view as measured from left to right that you can see when looking through your binoculars. In other words it is the width of the area that you can see from the binoculars.
In binocular terminology it is either specified in degrees or in feet. When we measure this in feet then it is known to be liner feet at distance of 1000 yards.
How does the binocular field of view matter?
The field of view matters as you need to choose an appropriate binocular based on the kind of needs that you have. You will need a wide angle of view in case you are watching a sportsperson on the football field. You will need to have a view whereby you can see the entire field. The same holds true for the birding binoculars. For birding binoculars also this is true as you need not focus generally solely on the bird but you need to have a major focus on the entire wide area where the birds are .
How much should be the field of view (FOV) ?
Lets us talk about the measurement in length. At a distance of 1000 yards you should be able to have a field of view of about 300 to 375 feet.
Talking about the angular degrees then most of the binoculars have an angular degree field of view between 6 degrees and 7.5 degrees.
As far as the angle conversion to feet is concerned it will mean that one angle degree is equal to 52.5 feet at a distance of 1000 yards.
Image credit Geodetic.com
Again when measured in degrees most of the times you will see the specification listing the two kinds of FOV. The first kind is the apparent field of view and the second one is the real field of view. For example if the real field of view is 5 degrees then the apparent field of view will be 5 degrees multiplied by the magnification of the binoculars. So in assuming a magnification of 8 will mean that the apparent field of view is 8×5 i.e. 40 degrees.
Tip: Most of the time the wide angle binos are the best but then it is always better to take into account the need that you have for the binoculars.