Each point on a scatterplot is, by default, shown as a small circle.

If you specify a marker variable, e.g. continents in a country data set, a different colour will be used for each of the continents.

When you select data points you can change the markers. Markers have a size, a border, and can be filled, several marker types are available.

Marker types:

All markers can be changed at the same time, but you can as well select individual points and change its marker to highlight a particular case of interest, select several points or, as shown to the left, use the lasso tool to select a group and then modify the selected case markers.