Timeframe
The timeframe is the period each candle on a chart represents: M1, M5, M15, H1, H4, daily (D1), weekly (W1), monthly.
The same market tells different stories depending on the timeframe. A 5-minute chart shows the session's noise, a daily chart the underlying structure.
Multi-timeframe analysis means starting with the highest one for context, then stepping down for timing. For example: trend on the daily, zones on H4, entry on H1 or M15.
Your main timeframe depends on your style and how much time you have. Someone with a full-time job who checks charts twice a day has no business scalping on M1. Signals on higher timeframes are generally more reliable, but rarer.
See also