histogram vs bar graph

histogram and bar graph both are nouns.

Word	Noun	Adjective	Verb	Adverb
histogram	Yes	No	No	No
bar graph	Yes	No	No	No

As nouns, bar graph is a hypernym of histogram; that is, bar graph is a word with a broader meaning than histogram:

histogram: a bar chart representing a frequency distribution; heights of the bars represent observed frequencies
bar graph: a chart with bars whose lengths are proportional to quantities

Other hypernyms of histogram include bar chart.

histogram (noun)	bar graph (noun)
a bar chart representing a frequency distribution; heights of the bars represent observed frequencies	a chart with bars whose lengths are proportional to quantities