A Greek letter, (δ: lower case, and Δ: upper case). Δ is often used to represent a difference,
usually a small difference. In calculus you talk about epsilon/delta ε/δ arguments for calculating
the limit of a series. You might also talk about delta files — the files that contain the differences
between two sets of files. These are typically much smaller than either set of files, and can be transmitted more
efficiently. JUnit has a method assertEquals( floatexpected, floatactual,
floatdelta). Here the word delta
means the tolerance, how close the numbers have to be to be considered equal.