When asked to do so, Broadcast will copy the custom fields of the post to the children. According to the WordPress Codex on custom fields, they are used to store meta-data about the post.
Normally all fields can be broadcasted without problems, but depending on which plugins are installed or your post workflow, you might want to handle some fields differently.
In the admin settings, Broadcast offers a custom field blacklist, a whitelist and a protect list. In these fields you can specify which fields you do not want broadcasted. If you do not want the fictional custom field
post_coauthor broadcast, just write its name in the blacklist, for example.
The fields also take wildcards: the fictional field above will be matched if you write
The blacklist will prevent the specified fields from being broadcasted.
The whitelist acts as exceptions to the blacklist.
The protect list will broadcast custom fields to the child posts only if the field does not already exist on the child. It does not update existing custom fields. This requires that the child post already exists.