Other forms: trendier; trendiest; trendily
Trendy describes something that's stylish or popular, like skinny jeans or fancy coffee drinks.
If your shoes are the newest, coolest kind of sneakers, they are trendy. If all of your neighbors seem to suddenly have Great Dane puppies, you can say that's a trendy dog breed in your neighborhood. Trendy is a relatively recent adjective, first formed in the mid-1960's from the noun trend, which originally meant "the way something bends," and later came to mean "general tendency."