Contact

A contact is the first vertical plug that joins a conducting film down to the silicon parts of a transistor.

Transistors do not speak metal by telepathy. A source or drain island needs a contact to metal. A gate often needs a contact to poly. The cut is small, the enclosure rules are fussy, and a misplaced contact lands on the wrong island and shorts a node. On the drawing it is a square even smaller than a via, perhaps 0.16 micrometer, sitting on active and covered by metal 1. A device with three contacts on the source is a current and reliability choice. People blur contact and via. The factory meaning keeps them apart: a contact reaches the devices, and a via climbs the metal stack. Both are cuts on their own layer. Sharing one contact between two islands that must stay apart shorts those islands, because the plug is a conductor and does not know your net names.

The square sits on the silicon island, and the metal strap lands on that square. The gate crosses the island beside it.

The plugs, the enclosure around them, and the sheet they belong to are covered in vias and contacts, enclosure, and what a layer is for.