stands for **gr**aphical **ob**ject, the generic drawing component in the grid framework of R graphics. Grobs can be very primitive, such as text, rectangles, lines, or complex objects such as full plots built up from many lower-level components.
The recommended grid package is included in every distribution of the R software. As such, it provides a low-level framework for building up all kinds of static graphics. The core component of grid-based graphics is a grob, which in its most basic form is a generic class of objects that describe a graphical component.
The most basic grobs are simple shapes such as pointsGrob, polygonGrob, etc., but new objects can be derived from those primitive objects, and are often assembled into a grob tree, or gTree, which holds together multiple shapes together with a specific layout.
Examples of high-level, complex grobs are the complete plots generated by the ggplot2 and lattice packages.
