The Latin word refrigerium literally means "refreshment," as Webster 1913 points out below. Refreshment is indeed what a modern refriger-ator does. But in ancient Rome, the word had a much more specific connotation: a refrigerium is a picnic in a graveyard.
The Roman practice of bringing food to the dead has its roots in the Greek perideipnon (literally "a meal nearby"). The surviving evidence suggests that the Greeks celebrated their funeral banquets in the homes of the bereaved, rather than at the place of interment; however, the peri in the word has led some scholars to believe that the very oldest rituals took place at the gravesite itself. At any rate, later Roman authors assumed that the Greek perideipnon was the equivalent of their mortuis cenam ("meal with the dead"), which did take place at gravesites.
The Romans believed that it was respectful to "refresh" the dead by bringing them food and drink. A refrigerium took place on the day of the burial itself (in which case it was called the silicernium); then again on the ninth day after the funeral. Every year afterwards, picnics were held at gravesites on certain holidays. The Parentalia, a festival honouring one's dead parents, and the Feralia, a festival honouring Jupiter (the "infernal"), were both characterized by graveside meals. According to a later Christian author, pagan Romans honestly believed that the dead were present and dining with them ("in convivio eorum quasi praesentibus et conrecumbentibus," De Testimonio Animae 4.5); this despite the fact that Roman religion did not have an especially developed sense of an afterlife.
Early Christians also engaged in a refrigerium ritual, but they did not always do it with their blood-families. Instead of (or in addition to) the pagan practice of honouring one's family members this way, the Christians took food to gravesites and to underground catacombs in order to honour the martyrs who were buried there. In a classic article in The Harvard Theological Review, George La Piana reproduces some of the touching, fragmentary inscriptions that second-century Christians left about their offerings.
AT PAVLVm
ET PETrvm
REFRIgeravi
There is even a catacomb in the region of St. Miltiades that is named The Crypt of the Refrigerium, where such meals took place.
To this day, Roman Catholic funeral services wish for locum refrigerii, lucis, et pacis, or "a place of refreshment, light, and peace," upon the dead. The term refrigerium, then, is not just any kind of refreshment, but rather the easing of a dead person's burdens. As a result of this "spiritualization" of meaning, the word is usually translated these days as "heavenly bliss" or something along those lines. Personally I still prefer the literal idea of a graveside picnic.
Just in time for Halloween.