The BitBake metadata has thousands of variables, but the scope where these variables are available depends on where it is defined. Basically, there are two kinds of variables as follows:
Variables defined in configuration files are global to every recipe. The parsing order of the main configuration files is shown as follows:
build/conf/local.conf
<layer>/conf/machines/<machine>.conf
<layer>/conf/distro/<distro>.conf
Variables defined within recipe files are local to the specific recipe only during the execution of its tasks.