The plot shows the Accuracy for each model for each cross validation model iteration. The solid black horizontal reference line is the median among cross validation iteration of the Accuracy values estimated without any model. The dashed horizontal reference lines above and below the solid one are the levels of the whiskers in a box plot for these no-model estimates. The better the model the larger the Accuracy, and a model whose cross validated Accuracy is near or below this baseline range is unreliable and should be ignored.