Some -- indeed many -- histograms relate to theoretical distributions. They're an entirely natural and conventional way for showing theoretical discrete distributions in particular, such as binomial or Poisson distributions. (But how well they do that is an interesting and sometimes important detail, yet is another story.) With theoretical include fitted, predicted or simulated distributions.
The words empirical distribution histogram I would explain as follows, even confidently without seeing any instances of quotations.
First, and trivially, distribution is redundant. All histograms show distributions. That's their job. I suppose in some instances people might want to insist that they are showing a distribution in a histogram, not something else in a bar chart. (To statistical people, a histogram is not a bar chart, itself yet another tiny story.)
Second, empirical just means based on observed data. Depending on context, that might be redundant too, or it might be helpful in contrast with, as said, a histogram of theoretical or predicted or fitted or simulated distributions.
Similarly with any plot: an empirical scatter plot is not a different kind of scatter plot. The writer or presenter is just flagging that it is based on data.
Yet again, I quite often see the term empirical cumulative distribution plot where empirical is sometimes helpful emphasis and sometimes unnecessary. (Cumulative can be omitted for some readerships.) But you can't understand ECDF plot easily (jargon popular in some fields) if no-one explains all the words behind it.
(I am all for concrete examples in most questions but in this one I think all that is needed is a dictionary-type explanation such as I am trying to provide.)
