There are many different views on the 5th precept. I'll sum up the 3 main views that I've encountered most:
In this article Bikkhu Bodhi explains that
The taking of intoxicants is defined as the volition leading to the bodily act of ingesting distilled or fermented intoxicants. It can be committed only by one's own person (not by command to others) and only occurs through the bodily door. For the precept to be violated four factors are required: (1) the intoxicant; (2) the intention of taking it; (3) the activity of ingesting it; and (4) the actual ingestion of the intoxicant. The motivating factor of the violation is greed coupled with delusion. No gradations of moral weight are given. In taking medicines containing alcohol or intoxicating drugs for medical reasons no breach of the precept is committed. There is also no violation in taking food containing a negligible amount of alcohol added as a flavoring.
In short, no alcohol. The only exceptions are when the alcohol is part of medication, or if one was drinking it unknowingly.
Trading or selling alcohol goes against the 5th Boddhisattva precept so that is a major offence.
Drinking alcohol still is an offence, but a minor one.
3. Less strict views
The less strict views on alcohol usually follow the reasoning that rules themselves do not lead to enlightenment and/or that the Buddha meant that for the 5th precept one should look at the intention of the person that is drinking. If the intent is to dull the mind or become drunk then it is an offence, otherwise it's ok.
There are 2 less strict views I'd like to mention explicitly here because I find them interesting.
- Mindful drinking
In the Tibetan Shambhala tradition apparently there is something called "mindful drinking":
once a meditator has developed basic Buddhist discipline ... the practitioner is ready to incorporate Vajrayana teachings, where the simple prohibitions outlined in the Sutras are re-evaluated. When a meditator reaches this point, which often takes a number years in the Shambhala tradition, a dangerous substance like alcohol is viewed as a potential aide for the practitioner. Within the context of strong discipline and clear intention, alcohol holds the possibility of no longer acting as a conventional escape, but instead being a tool for loosening the subtle clinging of ego.
- Strict rule only for monks
Some people have suggested that the "no alcohol"-rule only applies to monks, and for lay people it's more of a guideline or warning.
These are the six dangers inherent in heedlessness caused by intoxication: loss of immediate wealth, increased quarreling, susceptibility to illness, disrepute, indecent exposure, and weakened insight.
(source Digha Nikaya III, 182)
This can be seen as "nothing more than a warning". Also in the story of Svagata in the Divyavadana the Buddha said:
Monks, there are these and other transgressions involved in drinking alchol. That is why monks should not drink or distribute alcohol." (source).
This was after the monk Svagata appeared before the Buddha intoxicated, before that all monks were allowed to drink. The author of this article suggests that via interpretations of this story and the Buddha's teachings, later this monastic rule was changed into the 5th precept for lay people.