A build setting is a variable that contains information about how a particular aspect of a product’s build process should be performed. For example, the information in a build setting can specify which options Xcode passes to the compiler.

You can specify build settings at the project or target level. Each project-level build setting applies to all targets in the project unless explicitly overridden by the build settings for a specific target.

Each target organizes the source files needed to build one product. A build configuration specifies a set of build settings used to build a target's product in a particular way. For example, it is common to have separate build configurations for debug and release builds of a product.

A build setting in Xcode has two parts: the setting title and the definition. The build setting title identifies the build setting and can be used within other settings. The build setting definition is a constant or a formula Xcode uses to determine the value of the build setting at build time. A build setting may also have a display name, which is used to display the build setting in the Xcode user interface.

In addition to the default build settings provided by Xcode when you create a new project from a project template, you can create user-defined build settings for your project or for a particular target. You can also specify conditional build settings. The value of a conditional build setting depends on whether one or more prerequisites are met. This mechanism allows you to, for example, specify the SDK to use to build a product based on the targeted architecture.