Today I came across a Facebook post about weekend titled "Buen Fin". I know "happy weekend" translates as "buen fin de semana" and I reckon buen fin to be just an abbreviation. What I want to know from native speakers is, was this a one-off example that I came across or is it common for natives to abbreviate this phrase in real? Buen fin de semana does sound like quite a mouthful to me so I think buen fin would be a much easier way to wish someone a happy weekend. But I don't want to sound odd to native ears doing so.
The proper abbreviation for
Buen fin de semana in Spain is
Buen Fin has other meanings there:
Quiero llevar este proyecto a buen fin.
But is not used to refer to the weekend, at least in Spain.
It seems that in México
El Buen Fin is used to designate an special event:
El Buen Fin (Literally the "The Good End" but implying "The Good Weekend") is an annual nationwide shopping event in Mexico, in existence since 2011 and taking place on the third weekend of November in Mexico, and the beginning of the Christmas shopping season.
(Please, note the difference between the meaning of the expression and the implied meaning for the specific event)
So it is a sales/shopping event, like Black Friday (friday after Thanksgiving in the States), that takes place in a weekend. Probably what you saw in Facebook was an ad.
In my experience, “Buen fin” is a totally common phrase, meaning something like “Have a nice weekend”. The literal translation would be “Que tengas un buen fin de semana”, but few people say that because it's too long (but it may be appropiate in a formal context).
Also note that “fin” itself is also used with the meaning of “weekend”, such as “¿Qué vas a hacer este fin?” (“What will you do this weekend?”) and “¿Qué tal tu fin?” (“How was your weekend?”).
As Diego already pointed out, it's probable that what you saw actually was an ad for El Buen Fin, a Black-Friday-like event. The name of this event is such because people already say “buen fin”, and they want to convey that a nice weekend will be a shopping weekend.
Edit: I think the confusion with Diego is that he is from Spain and I'm from Mexico. It seems that it's a Mexican idiom rather than a generalized one.