I've found yet another PDF that describes the problem. This one describes "mura" this way:
One large category of defect is called “mura,” derived from the Japanese word for blemish. Mura are typically low-contrast imperfections that are larger than a single pixel, and are visible when the display is driven at a constant gray level. They may be caused by non-uniform distribution or impurities of liquid crystal or mechanical imperfections in the display assembly.The article, "Flat Panel Display Defect Measurement Using a Human Vision Model," by NASA scientist Andrew Watson, was mentioned in this post in the Official Sony 46" XBR LCD Uneven Backlight/Cloudy Thread, at www.avsforum.com.
A longer article by Watson, "The Spatial Standard Observer: A Human Vision Model for Display Inspection," can be found here. This article brings home to me the fact that mura defects exist in a range of severities measurable in units of just-noticeable difference (JND). A 1-JND mura is barely noticeable when the display is driven at a uniform gray level; it may well be undetectable when a regular picture is on the screen. On the other hand, a mura with a measure of 4 JND would be quite detectable. It would, I assume, affect a regular picture on the screen.
Some illustrations in these articles depict TV screens with faint vertical-band mura defects that look like mine do. But they also have small "blobs," as I call them, while mine has no blobs. It is the nonuniform blobs which are of concern to the article's author. The faint vertical bands are apparently considered insignificant.