Inconsistency means a lack of agreement or reliability between things that should match up. When your friend says she'll meet you at the park every Saturday but only shows up half the time, that's inconsistency. When a referee calls a foul on one team but ignores the exact same action from the other team, players notice the inconsistency in how rules are applied.

The word often points to contradictions or unpredictability. If a teacher is inconsistent, she might be strict about tardiness one week but ignore it the next, leaving students confused about what the actual rules are. A basketball player who scores twenty points one game and two points the next shows inconsistency in performance.

You might notice inconsistencies in a mystery story when the detective realizes two witness statements don't match, or when facts contradict each other. Scientists look for inconsistencies in data that might reveal errors in an experiment.

The opposite is consistency: showing up reliably, following the same principles, or making sure facts align.