Brushing

Perhaps the most common and historically first widely used technique explicitly identified as graphical exploratory data analysis is brushing, an interactive method allowing one to select on-screen specific data points or subsets of data and identify their (e.g., common) characteristics, or to examine their effects on relations between relevant variables (e.g., in scatterplot matrices) or to identify (e.g., label) outliers.

See also Brushing dialog, Brushing - Extended tab,  Glossary of Brushing Terms, and Exploratory Data Analysis and Data Mining Techniques.