Switch box (switch block)
Beginner
A spot where wires cross in an FPGA. Tiny switches there decide which wires join.
Novice
The set of programmable switches where a horizontal and a vertical routing channel meet. Each one lets a wire segment connect to segments on the other sides.
Expert
Characterized by its flexibility Fs (often 3) and pattern (disjoint, Wilton and others). With multi-length directional wires, switch and connection boxes merge into per-wire driver muxes.
Explained in Lookup tables and the FPGA fabric (Architectures).
See also: Routing fabric (programmable interconnect).