Laptop computer half-height mini PCI Express Wi-Fi network card. Fits inside the dedicated socket in some older laptop computers, connected to their built-in antenna, to provide a Wi-Fi connection. I bought it (used) to upgrade a family Lenovo ThinkPad but found out my model needed a full-height card instead. It was cheap enough not to be worth posting back for a refund.
Ruler in one photo is to show the scale, and is not included!
Laptop Wi-Fi card (Fulbourn CB21)