Certainly not a “slang” word but just one of those mysterious Romanian words with a shadowy and uncertain past, ajun simply means the day (or night) before an important event.
In this case, Ajunul (“the day/night before”) Craciunului (“of the Christmas”) simply means the night/day before Christmas, or as it is said in English, Christmas Eve.
If you speak Romanian, I found this religious tale about Christmas Eve, wherein God (in the form of an angel) visits a single mother who puts animal feces (Rom: baliga) into the oven to “feed” her kids. As with most Romanian stories, very graphic imagery is involved.
Dumnezeu i-a zis:
– Haide femeie, deschide cuptorul si scoate mancarea, ca de acum s-o fi facut.
– De ce va bateti joc de mine? Parca domniile voastre nu stiti ce am pus in cuptor spuse femeia plangand.
– Nu auzi ce ti-am spus? Deschide! insista Dumnezeu.
De gura strainului, femeia a deschis cuptorul, si nu mica i-a fost mirarea cand a vazut tot felul de bunatati inauntru, la fel ca pe vremea cand traia barbatul ei.
Just like when her man was alive :P
AND NOW YOU KNOW!