A Violin Plot is used to visualise the distribution of the data and its probability density.
This chart is a combination of a Box Plot and a Density Plot that is rotated and placed on each side, to show the distribution shape of the data. The thick black bar in the centre represents the interquartile range, the thin black line extended from it represents the 95% confidence intervals, and the white dot is the median.
Box Plots are limited in their display of the data, as their visual simplicity tends to hide significant details about how values in the data are distributed. For example, with Box Plots you can't see if the distribution is bimodal or multimodal. While Violin plots display more information, they can be more noisier then a Box Plot.
http://datavizcatalogue.com/methods/violin_plot.html