This article is from the Real Ale FAQ, by with numerous contributions by Brett Laniosh others.
Please be aware that exact definitions are not possible. The explosion in
smaller brewers experimenting, making this especially so. Always look at
the pump clip because for example some 'milds' eg. Sarah Hughes, are
Ale: A beer brewed with a top-fermenting yeast. It used to refer to a beer
made without hops but this is not the case now.
Bitter: A highly hopped beer and the most common type of draught ale.
Bitters can range from below 3.5% up to 5% ABV.
Brown ale: A bottled, lightly hopped and sweetish mild ale. Usually lower
in gravity though there are exceptions.
Heavy: A Scottish and North East term for a medium strength beer usually
light in colour!
A: India Pale Ale. Strictly speaking a high strength pale ale for export
but the term is commonly used for light bitter ales.
Lager: A British term for a continental beer made with a bottom fermenting
yeast using different malt and hops than most bitters. They undergo a long
secondary fermentation at a low temperature. Most British lagers are weak,
inferior versions of their mainland Europe namesakes.
Light ale: A low gravity bottled ale. Scottish light ales are usually dark
Mild: A lightly hopped beer, often dark in colour and usually low in
Old ales: See Winter ales.
Pale ale: A medium gravity bottled ale. The term is used in the South West
to refer to low gravity draught ales.
Porter: A dark and sweetish but well hopped beer.
60/-, 70/-, 80/-, 90/-: 60 shilling, 70 shilling, 80 shilling, 90 shilling
ale, all terms for Scottish beers. They equate, very roughly, to mild,
light, heavy and strong.
Stout: Usually very dark, heavy and well hopped beer. Dry tasting with
a creamy head. Though the term is no longer used, "Milk" Stout is
thought to have been so named because it contained lactose, a sugar
derived from milk. As lactose cannot be fermented by yeast, the sugar
stays in the beer.
Wheat beer: A beer originating from Bavaria where it is known as Weizen.
The wheat is added to the mash and results in a refreshing summer drink.
Both pale and dark versions are available, some are brewed to be drunk
hazy, some brewed to be drunk clear.
Winter ale: Usually a high gravity and full-flavoured beer sold during the
winter months. The name is now synonymous with "Old ale".