Abstinence means generally voluntary restraint from something, while teetotalism means especially the complete abstinence from alcoholic beverages.
Reasons for teetotalism may be, for example, religious prohibition, as in the Islamic culture, a voluntary renunciation, for example, to avoid the potential risk of alcohol consumption or even to the calories contained in alcohol, or a necessary renunciation, like in cases of diabetes or liver diseases or to prevent recidivism after a successful alcohol withdrawal.
For the latter group, the often weak-willed peoples may have maintained their teetotalism with the aid of medicaments like Antabus or Campral.
The concrete proof of teetotalism can be necessary for the re-issue of the driving licence or in custody disputes. This can be achieved by hair analysis (determination of fatty acid ethyl esters and / or ethylglucuronide).
Teetotalers can be organized in self-help associations. The most famous is likely the Internatioanal Organization of Good Templars (IOGT).