A light-dependent resistor (LDR) is a component whose resistance changes with the brightness of the light falling on it. Light intensity is a measure of how bright the light is.
In bright light the resistance of an LDR is low. In darkness the resistance is very high, so only a small current passes. So as the light intensity increases, the resistance of the LDR decreases.
Because the resistance changes, the current through an LDR also changes. If the potential difference across it stays the same, a lower resistance means a larger current. This makes LDRs useful as sensors, for example in a circuit that switches a street light on when it gets dark.
