Style Tiles are the wonderful visual concept created by Samantha Warren that help form a common visual language between the designers and the stakeholders. This can then be used as a catalyst for conversations between the client and the designers.
Style Tiles are a design deliverable consisting of fonts, colors and interface elements that communicate the essence of a visual brand for the web.
On the website Styletil.es Samantha describes them as:
Style Tiles are similar to the paint chips and fabric swatches an interior designer gets approval on before designing a room.
An interior designer doesn't design three different rooms for a client at the first kick-off meeting, so why do Web designers design three different webpage mockups?
The site itself will provide you far more information, plus a super hand PSD template to download. Check out Style Tiles!