What does Boxing Day have to do with boxing?
A computer architecture in which, within a given 16- or 32-bit word, bytes at lower addresses have lower significance (the word is stored "little-end-first"). The PDP-11 and VAX families of computers and Intel microprocessors and a lot of communications and networking hardware are little-endian.
The term is sometimes used to describe the ordering of units other than bytes; most often, bits within a byte.
Compare big-endian, middle-endian. See NUXI problem.