SharePoint content Types ghostable / unghostable

basically, let's know some definitions:

content type: is a way to group site columns into a reusable group with some basic settings e.g.

associate document template to your content Type .  

content Type Hub : is a way to centralize your content types to use across site collections.

There are two types of content types:

site Content type : that is a template and saved in site collection content types gallery.

list content type : Is instance of content type on  a list.

There are two ways for creating Content Types in sharepoint :

1- using GUI/Custom Code : that is mean that your content type definition in the sharepoint database only. So it is named unghostable content type.

2-Using  Feature/CAML : content type will deployed in the feature XML under 15-hive so your site content types is ghosted so you will expect that when updating your content type XML definition under 15-hive it will reflect in your content type directly.

But there is an issue in List content types are instantiated by code so will be in a database only that mean when you change site content type definition your lists which used this content types will not change.