Preci-Dip
Preci-Dip connectors are a series of electrical connectors used primarily to connect primarily between printed circuit boards (PCBs). Preci-Dip connectors are sold in large pin counts (often rows of 64) but can typically be broken into lengths of an arbitrary number of pins. Preci-Dip connectors have a 0.1" spacing between pins, which is a common standard on microcontrollers such as most Arduino and Teensy boards.
"Zero Profile" Sockets
Unlike standard 0.1" connectors, Preci-Dip headers have very small yet strongly mating pins, greatly reducing the required socket height. Both low profile and "zero profile" sockets exist; the "zero profile" versions are small metal receptacles which are soldered through holes in a PCB, having depth below the board but no meaningful height above it. This greatly reduces the minimum required mating height, allowing very fine control over the spacing between parallel connected circuit boards.