A compression or contraction is a transformation in which a figure grows smaller. Compressions may be with respect to a point (compression of a geometric figure) or with respect to the axis of a graph (compression of a graph).
Some high school textbooks use the word dilation to refer to all transformations in which the figure changes size, whether the figure becomes larger or smaller. Compression refers to transformations in which the figure becomes smaller. Dilation in contrast, properly refers only to transformations in which the figure grows larger. Unfortunately, the English language has no term that refers collectively to both stretching and shrinking.
“Compression.” Mathwords, www.mathwords.com/c/compression.htm.