The dots style plots a tiny dot at each point; this is useful for scatter plots with many points. Either 1 or 2 columns of input data are required in 2D. Three columns are required in 3D.
For some terminals (post, pdf) the size of the dot can be controlled by changing the linewidth.
1 column y # x is row number
2 columns: x y
3 columns: x y z # 3D only (splot)