The trade dress of a product can be its source-indicating packaging, materials, configuration, design, decor, colors, and/or shape.  

For example, a soda bottle having certain hour-glass-like curves will be instantly recognized by most consumers as a Coca-Cola bottle.  Likewise, the shapes, materials, and colors of certain smart phones instantly identifies them as iPhones from Apple.  And recently, courts have begun treating as trade dress the "look and feel" of certain user interfaces, such as websites.

Because trade dress can serve as a source identifier, it can be protectable as a form of intellectual property under federal law, much like a trademark.  The legal protections provided to trade dress law are intended to protect consumers from unwanted imitations, that is, to help consumers avoid mistakenly buying a product that is mimicking what the consumer really wanted to buy.  

Just as with trademarks, although not required, there are many advantages to registering a product's trade dress with the USPTO.  And just as with trademarks, one of the significant registration requirements is that the trade dress be distinctive, that is, not improperly descriptive.

But trade dress law requires something more.  To be registerable, trade dress must be non-functional.  That is, even if the packaging, materials, configuration, design, decor, colors, and/or shape of a product are distinctive, they must not provide any substantial function other than to indicate the source of that product.