In Ireland a standard drink, also called a unit of alcohol, has about 10 grams of pure alcohol in it. In the UK, a standard drink has about 8 grams of pure alcohol.
Here are some examples of a standard drink:
A pub measure of spirits (35.5ml)
A small glass of wine (12.5% volume)
A half pint of normal beer
An alcopop (275ml bottle)
A bottle of wine at 12.5% alcohol contains about seven standard drinks.