Days Since Played is a new "calculated" field based on the Last Played field. Days Since Played will, unsurprisingly!, return the number of days since you last played a track. (If you have never played it, it will return -1.)

You can both filter/search and sort on this field. For example, you set up a playlist that only includes tracks it has been more than 3 months since you played:

This field is also displayed in the explorer, for example: