These abbreviations are short for, respectively, yellow bubble and slightly yellow bubble. They are used chiefly in reference to carded action figures, and specifically to the clear plastic bubbles that hold the figures to their blister cards. These have a tendency to yellow over time, especially those issued in the later stages of the vintage line, during the Return of the Jedi and Power of the Force series. But yellow bubbles have appeared on all types of carded figures, from the Star Wars to the Droids and Ewoks series, and even on some other types of toys, such as the three POTF Body Rigs.
How can the yellowing of bubbles be prevented? It can't, unfortunately-- many bubbles seem to yellow without cause; even figures that have been pulled directly from sealed cases have revealed themselves to have yellow bubbles. Your best bet is to keep your figures out of direct light and in a stable environment. And pray.
Of course, it goes without saying that a figure with a yellow bubble--even one that is only very slightly tinted--is substantially flawed, and its value on the open market will reflect that.
Description: Ron Salvatore