Trend in a price chart is the most simple yet most important concept of technical analysis. There are 3 possible trends: Uptrend, downtrend and sideways.
Uptrend: When we have at least 2 consecutive higher highs and higher lows.
Downtrend: When we have at least 2 consecutive lower highs and lower lows.
Sideways: When there is no uptrend or downtrend.
We can define trends by designing trendlines. In uptrends we join the higher lows to form the trendline. In downtrends we join the lower highs.
Trendline in uptrend
Trendline in downtrend
A trendline can be support or resistance