This is an SMD socket for a SmartCard. SmartCards are plastic cards with an embedded chip used to store any data you want. SmartCard applications are limitless; and they're growing increasingly popular, showing up on credit cards and other common identification cards.
A standard credit-card sized plastic card (53.98mm width) should fit snuggly. The socket forms a physical connection with the eight contacts on a SmartCard. See the datasheet below for pin-out and dimensions. The pads are spaced by 0.1".
Breakout board coming soon!