The period each candle represents on a chart, from one second to one month.
How timeframes stack up. A daily candle is not different data, only coarser data: it opens where the first six-hour candle opened, closes where the last one closed, and its wicks reach the highest and lowest prices any of the four touched.
A trend on one timeframe can be a pullback on a higher one. Multi-timeframe analysis means picking a higher timeframe for direction, an intermediate one for the setup, and a lower one for the entry.
Lower timeframes have more noise and more trades; higher timeframes have fewer signals and larger stops. Neither is better, but mixing them without a plan is a common cause of confusion.
Example: a swing trader uses the weekly chart for trend, the daily for the setup, and the hourly for entry timing. A scalper might use 15-minute, 5-minute, and 1-minute.