Nice simple and plain post from statgraphics.blog.com, explaining what histograms are and why they are different from barcharts:

Histograms are often mistaken with barcharts. The fundamental distinction between the two is:

• Barcharts show counts (or weights) for the discrete axis of a categorical variable
• Histograms show an approximation of the density function (if scaled accordingly) of a countinuous variable.

Histogram	Barchart

That's absolutely right, even if I didn't ever realize it, I used to mix the two names up too.

And there's more:

As a consequence, the only thing that can be quantified in a barchart is the bar height ... On the other hand, in a histogram, the area of the boxes is proportional to the density approximation. If all bars have the same width in a barcharts, or gaps are drawn in a histogram (which is complete nonsense), the two plots can get mixed up.

I would also add that another consequence of that is that the values in barcharts can be reordered to show different patterns. The most common ways are: order by frequency or alphabetical order, but there can be others available.

Barcharts and histograms does not look "cool" enough but they are among the most powerful visualizations available. If used properly, they can convey a lot of information in a compact and effective way.