A timeframe is the scale of the chart. On a five-minute chart, every small fluctuation is visible; on a daily chart, the same fluctuations are compressed into a single candle and simply disappear from view. The same market can look opposite on different timeframes: on the hourly chart, there is a steady decline, while on the weekly chart, this is just a pullback within an uptrend.
From this comes a rule that saves a lot of money: first, the higher timeframe and the overall direction are determined, and only then is an entry point looked for on the lower one. Trading against the higher chart is possible, but it requires much more precise work with the stop.
The timeframe directly determines the behavior of indicators. The same indicator with the same settings on a minute chart will trigger dozens of times an hour, while on a daily chart it will give a few signals a month. Therefore, settings are almost always chosen for a specific 'asset plus timeframe' pair, rather than being taken as universal.
Timeframe choice should also fit the trader's lifestyle. Minute charts demand constant screen time and quickly become exhausting, while daily charts may require a decision only once a day. A mismatch can be costly: traders may damage an account not because the method is flawed, but because its pace is impossible for them to sustain.
