A sensor array is a group of sensors deployed in a certain geometry pattern. The advantage of using a sensor array over using a single sensor lies in the factor that an array can increase the antenna gain in the direction of the signal while decreasing the gain in the directions of noise and interferences. In other words, sensor arrays can increase signal-to-noise ratio (SNR): magnify the signal while suppressing the noise. Another ability of sensor array is that is can detect the direction and distance of impinging signal sources. The technology to achieve this is called Array Signal Processing.
The sensor array can also help to defining a beam to focus analysis in one part of the space, this is widely use for Radar. The selection of sensors help you focusing in one direction, increasing the signal to noise ratio and helping you for the separation of the detected points.