Cargo profiles are predefined configurations in Cargo.toml that control how your code is compiled, such as optimization levels and debug information. You customize them by adding a [profile.*] section to your Cargo.toml file and setting specific options like opt-level. For example, to increase optimization for the development profile, add the following to your Cargo.toml:
[profile.dev]
opt-level = 1
This overrides the default opt-level of 0 for the dev profile, making your development builds slightly faster to run at the cost of longer compile times.