Something unplanned happens without anyone having arranged it beforehand — no schedule, no decision, no preparation. It covers a wide range of feelings depending on what it describes. A trip that turns into an unplanned night in a small town can be a happy accident, the best part of the holiday. An unplanned stop, an unplanned delay, unplanned expenses, an unplanned power cut: those are the awkward kind, things that pushed into your day uninvited. And there is one very common set phrase you should know because people say it carefully: 'an unplanned pregnancy'. English chose 'unplanned' here on purpose, because it is gentler and less judging than older words like 'accidental' or 'unwanted' — it says only that this was not arranged in advance, and nothing about whether the baby is welcome. Grammatically it sits happily before a noun ('unplanned changes') or after be ('the meeting was completely unplanned'). Compare it with its neighbours: 'unexpected' is about surprise — you did not see it coming; 'unplanned' is about arrangement — nobody set it up. They often overlap, but not always. You can fully expect an unplanned expense to appear at some point without having planned any particular one.