Definition from the Coin World web site:

Filled dies: The Mint factory has its share of dirt, grease and other lubricants, and metal filings. The recessed areas of the dies sometimes fill up with a combination of this foreign material, preventing the metal of the coins from flowing into the incused areas. This results in weak designs or missing design details. The filled-die coin is one of the two most common types of errors. Filled-die coins are a form of struck-through error.

Here's an example of a token manufacturing error seen from time to time. The example on the right is what they were trying to make. The one on the left with the "mushy" detail is probably from striking with grease-filled dies. The other side doesn't exhibit the problem. Now that I look at the detail in the scan, I believe the other token also shows some evidence of the same problem near the bottom.

This is one of the more original designs for a gaming token. There apparently was an attempt to put every known Nevada historical symbol somewhere in the design [g].

Although there is no mint mark, Janice's token list shows it was made in 1979 by Roger Williams Mint (RW).