For puzzles which ask the solver to determine a hidden property of certain words (or phrases), given a set of words with that property and usually also a set of words without it for comparison. Puzzles with this tag often have titles of the form "What is a [...] Word™?"
Use this tag for puzzles in which the goal is to discover a certain secret property of certain words (or phrases), whose nature is hinted at by a list of words which possess that property, and often also for comparison a list of words which don't.
Since July 2015, puzzles with this tag usually take approximately the following form:
Title: What is a XXX Word™?
If a word conforms to a special rule, I call it a XXX Word™.
Use the list of examples below to find the rule.
[list of XXX words]
[list of non-XXX words]
in imitation of the style established by the user JLee in the puzzle What is a Cyclone Phrase™? and others written in the same style which followed it. XXX is normally an adjective which cryptically describes the word property which solvers are expected to find. The property can be pretty much whatever you like: it can be about the meaning of the word, the letters within it, or anything else.
Sometimes this tag can also be used for puzzles about properties of phrases instead of words, as in the above-linked Cyclone example, but most commonly it's about properties of individual words.