The Zerg Nydus Canal is a structure whose exact origin is unknown, and the exact process of its operation is a mystery. Of what is known however, the canal serves as a quick transport link from one location to another. The Canal needs two anchoring points, entrance and exit nodes, but once both have been set down, the Zerg forces can travel both ways. Only one Zerg ground unit can be transported at a time, but the process is quick and a large force can travel through in a matter of seconds. The Nydus Canal also has the interesting ability of being able to place its exit node on the Creep of any Zerg colony, friendly or not, which can allow a player to secretly start building a nydus canal in an enemy base. If successful this player can mass his units at will into the opposing player's base.
Underwood, Peter, Bill Roper, Chris Metzen and Jeffrey Vaughn. StarCraft (Manual). Irvine, Calif.: Blizzard Entertainment, 1998