Ampro is probably right about a trend, and Trader333 is right about the occurrence of a market trend.
A trend is considered formed when a few consecutive candlesticks / bars in a row show a clear direction ( either up or down ). Just like distribution of dots on a graph of lab experiment, a mean line drawn passes those candlesticks/ bars show the trend. It is more like the direction of a moving average line, irrespective of the time frame of the chart.
Example, my old work on a liquid US stocks, shows that 30 or more consecutive candlesticks / bars in a row, on a chart are good enough to indicate a trend. Variation of course exists on the illiquid stocks.
But this trait is not really similar on the major forex currency pairs. Difference market, particularly different currency pairs, has different dynamics, although some common and repetitive traits do exist among them.
A retracement ( pullback ) of a bullish rally ( uptrend ) on a 4- hour chart, if reduced down to 1-hour or 30-min chart, may show a clear ( and exploitable ) bearish rally ( downtrend ).
A rebound of a bearish rally ( downtrend ) on a 4-hour chart, if reduced down to 1-hour or 30-min chart, may show a clear ( and exploitable ) bullish rally ( uptrend ).
One thing for sure, a trend is formed only after a consecutive extension of price movement.
( In hindsight ), we may occasionally find a few minor bullish or bearish rallies at 1-hour chart, in a ranging market as shown on a 4-hour chart or chart of higher time frame.
Just like stock, in forex, we do have short-term, medium-term and long-term trend, based on different time-frame of a chart. Of course the exact definition of a trend is still very subjective and without a clear boundary.
Just my 2-cent...