Feature histogram enables a single glance to view each features general distribution split between the labels categories.
For continuous features, the x-axis of the histogram shows the feature values while the y-axis shows the density (local amount normalized by the total amount).
The separate histograms depict the different labels of the samples (in the example bellow, the samples with the positive label vs. the negative label)
For categorical features, the x-axis of the histogram shows the density of the samples with
each such category while the y-axis shows the categories. The stacked bars denote the different labels of the samples.