Support is the price level at which demand is thought to be strong enough to prevent the price from declining further.

Resistance is the price level at which selling is thought to be strong enough to prevent the price from rising further.

Some important things to keep in mind, strong support occurs where a downtrend is expected to pause due to a concentration of demand. Strong resistance occurs where an uptrend is expected to pause temporarily, due to a concentration of supply.

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Support and Resistance Levels