A setup is not a hunch or a general market view. It is a checklist: the instrument, the timeframe, the structural condition, the location, and any required confirmation. If it cannot be written down and applied by another person to the same chart, it is not a setup yet.
Precision matters because it is what makes review possible. Only a defined setup can be counted, tested, and judged over a meaningful sample-size. Undefined discretion produces a trading record you cannot learn anything from.
A setup is separate from the trigger, which is the event that puts you in, and from trade management, which decides what happens afterwards. Mixing the three is a common reason traders cannot tell whether their problem is selection, timing or exits.
Related: trigger, invalidation-level, trade-location, discretionary-vs-systematic, trading-plan