A crate is the smallest amount of code that the Rust compiler considers at a time. It can be a binary crate or a library crate.
A binary crate is a program you can compile to an executable that you can run, such as a command-line program or a server. Each must have a function called main that defines what happens when the executable runs.
A library crate doesn't have a main function, and it doesn't compile to an executable. Instead, it defines functionality intended to be shared with multiple projects.
A package is a bundle of one or more crates that provides a set of functionality. A package contains a Cargo.toml file that describes how to build those crates. Here is an example of a package that contains a binary crate and a library crate:
$ cargo new my-project
Created binary (application) `my-project` package
$ ls my-project
Cargo.toml
src
$ ls my-project/src
main.rs
lib.rs
The package contains the binary crate my-project, which is defined in src/main.rs. The package also contains the library crate my-project, which is defined in src/lib.rs.
The Cargo.toml file in the package describes how to build the binary and library crates. It also specifies that the library crate is the dependency of the binary crate.
This is just a simple example of a package. Packages can be much more complex, but they all follow the same basic structure.
