Alcopops is a term created by popular media to describe bottled alcoholic beverages that resemble drinks such as soft drinks and lemonade. Malternative is another name used for these drinks and is a reduction of the phrase 'malt alternative,' and it implies that these drinks are meant to be an alternative to that slightly more famous category of malt-based beverages: beer.
These drinks begin life much the same way as beer: Malted grain and water are fermented to create alcohol. The resulting mixture is then filtered (generally with carbon) to remove any "malt" flavor, and then sweet fruit flavorings are added. Alcohol content is generally around 5% by volume.
The resulting concoction is sweet, like a soft drink, comes in 12 ounce bottles, like beer, is marketed heavily to the "under 30" crowd, especially women, and, perhaps most importantly, is regulated the same as beer.