What is a histograph and plotting after groupby

Hi all,
please enlighten me on the following:

  1. a histograph looks just like a bar chart, so what is the difference between plotting the data using bar graph vs histograph?

  2. when using groupby on a dataframe, example: df.gropby(df.age)[‘name’].count().plot.bar(); what is being used to plot the bar chart? is it matplotlib or seaborn? how do I set the fontsize, legend details etc if the bar graph is plotted this way?