The Coded Width that can be found in many files, is a subset of the general width of a file. Similar to the other subsets like the image width or cropped image width, the Coded Width specifies a specific width within the file.
In case of the Coded Width, it expressed the width of a video file, picture or photo, document or even parts of an audio file (e.g. the cover art) as it is coded within the file. This can and usually does differ from the original width of the file and is altered to fit within a certain standard or requirement.
Together, the Coded Width and the Coded Height form the coded dimension of the file.