Resistance level is the price level, which, historically, a security has had difficulty going above. Typically, the resistance level can be thought of as the level at which many buyers tend to sell a security. Resistance levels are often used in technical analysis. 
It is where the price tends to find resistance as it is going up. This means the price is more likely to "bounce" off this level rather than break through it. However, once the price has passed this level, by an amount exceeding some noise, it is likely that it will continue rising until it finds another resistance level.