I guess a temporary chair table is what it should be called. My wife and I often, especially on the week-end, sit in our easy chair in the sun room and have a sandwich or snack for lunch . This board lays across the chair arms to make a temporary table for our food and a resting place for our nook reader or a book.
The one on the right my wife bought several years ago. I made the other from some scrap pieces of cedar. When not in use it sits on the floor in the stand beside our chairs ready to use.
Of course, she wanted the cedar one I made.