Bar charts are for discrere data. That is, can only take particular values, eg number of children, which can only take a whole number, or favourite football team for instance. They typically have gaps between the bars to indicate the separateness of each value.
Histograms are either continuous (height) or grouped discrete data and don’t have gaps between the bars. Also, with Histograms, since the width of each bar is not necessarily the same, the area of the bar and not its height indicates the frequency
