Scaled

Scaled[{x, y, ...}]
gives the position of a graphical object in terms of coordinates scaled to run from 0 to 1 across the whole plot range in each direction.

Scaled[{dx, dy, ...}, {x₀, y₀, ...}]
gives a position obtained by starting at ordinary coordinates {x₀, y₀, ...}, then moving by a scaled offset {dx, dy, ...}.

MORE INFORMATION

Scaled can be used to specify scaled coordinates in any two- or three-dimensional graphics primitive.

You can use Scaled to represent objects that occupy a fixed region in a plot, independent of the specific range of coordinates in the plot.

Scaled refers only to the region of a plot defined by its PlotRange and PlotRangePadding. It does not take account of elements such as tick labels, or of margins introduced by PlotRangeMargins.