A truffle package is a collection of smart contracts and their artifacts. A package can depend on zero or more packages, that is, you use the package's smart contracts and artifacts. When using a package within your own project, it is important to note that there are two places where you will be using the package's contracts and artifacts: within your project's contracts and within your project's JavaScript code (migrations and tests).

Projects created with truffle have a specific layout by default, which enables them to be used as packages. The most important directories in a truffle package are the following:

• /contracts
• /build/contracts (created by truffle)

The first directory is your contracts directory, which includes your raw Solidity contracts. The second directory is the /build/contracts directory, which holds build artifacts in the form of .json files.

Truffle supports two kinds of package builds: npm and ethpm packages. You must know what npm packages are, but let's look at what ethpm packages are. Ethpm is a package registry for ethereum. You can find all ethpm packages at https://www.ethpm.com/. It follows the ERC190 (https://github.com/ethereum/EIPs/issues/190) spec for publishing and consuming smart contract packages.