Generally this is a file context type that is usually set on files that need to be shared among certain domains and where the administrator wants to manually manage the type.
The use of customizable types is deprecated as the preferred approach is to use semanage(8) fcontext(8) ...(8). However, SELinux-aware applications such as setfiles(8) will use this information to obtain a list of types relating to files that should not be relabeled.
selinux_customizable_types_path(3) will return the active policy path to this file. The default customizable types file is:
Where {SELINUXTYPE} is the entry from the selinux configuration file config (see selinux_config(5)).
is_context_customizable(3) reads this file to determine if a context is customisable or not for the active policy.
Where: