Little red party dress
Not that a party dress have to be red and short, but it sure helps drawing looks to you.
In what way do party dresses differ from ordinary every day dresses? Well, they usually look more expensive and are often very detailed or have ornaments on them. A party dress is not a party dress either. It all depends on what party we are talking about. Is it a formal party? Is it a school party? A bachelor party? A Christmas party? A birthday party? Or maybe it's a garden party with your friends where a light and floral party dress might seems the most fit.
When it comes to formal dresses, they tend to be kind of glossy in the fabric. Maybe satin like, and long. Usually they come with a matching scarf. To really make a complete outfit for a formal party, you also need a matching purse of some sort. Here's a site containg a lot of purses, or vesker as they say.
Too find the perfect party dress, you should look for sites specializing in dresses. You could of course look at a web shop, but the variety are usual much broader if you visit a comparison site or a dedicated site, like festkjole, containing a lot of party dresses for your choosing.