Slot 2 appears to be a PCIe x1 slot. You can use it for WiFi cards as an example or any device that requires a PCIe x1 slot. This web page should help. There are adapter cards that can be used for a PCIe SSD.
What is Slot 2 used for?  Cannot find it in the manual looking to expand[IMAGE] either SSD, HD, etc...
What is Slot 2 used for Inspiron 3880