Binning is a special clocking scheme for area sensors. The horizontal lines are summed vertically in the chip. Here the chip acts like it has only one line like a line sensor. That leads to a higher signal level by the same read noise.
If a line signal has only one dimension, like in spectrometry, the binning can improve the signal to noise ratio. The software is capable of selecting a range of lines for a partial binning. That means that those areas of the sensor which have no optical signal can be omitted and only the lines of interest are used for the sampling. All other lines are discarded. All area sensors from Hamamatsu (FFTs) can be used in this binning mode. Also the EM sensor TC253 can be used in this binning mode.
Shown here is a spectra sampled with a TC253 sensor from TI. The sensor has 656 x 496 pixel with em- amplification and free adjustable binning. It is a 100 times amplificated HG line spectra (green line and yellow double line)