Economy is a major feature added in Version 1.192.0. Players can disable or enable Economy in the World Settings. There is also an Category:Economy Deluxe Pack DLC.

For all games, the Economy update added player-to-player trading, inter-faction reputation, and a currency. Economy blocks let players manage (NPC-generated or player-made) Contracts and sales offers. Safe Zone blocks protect trade stations from raids.

Additionally, enabling the "Economy" option in the World Settings will make NPC-owned Trading Outposts encounters spawn in the world where NPCs offer goods and contracts, including uncraftable trade items (Medkit, Powerkit, Clang Cola, Cosmic Coffee).

The Economy features can be used in multiplayer and singleplayer games, but specifically player trading and player contracts obviously only make sense in multiplayer — no NPCs will ever come and accept your contracts/trades in singleplayer.