Migration means to move all (or better to say, as much as possible) your data from a previous forum software to flarum. Essentially a migration tool for flarum should import all data managed by the core and the core bundled extension, which are (plz correct me out there if I am forgetting something):
- users data, credentials and avatars
- user groups
- user permissions
- categories and boards (which flarum manages as Tags)
- discussions
- posts
This leaves out other data which flarum core does not support directly, but can be be adding 3rd party extensions. Some example:
- personal messages, still not supported
- Image attachments (other file types not supported by any extension at this moment)
- polls, still not supported
- favourite/bookmarked posts/discussions (not supported by any extension at this moment)
- basically anything else
Be advised that porting your data to any new platform, flarum or any else, is a major effort with possibility of data loss and partial import only of certain data if the features of your former forum are not implemented or are heavily changed in flarum.
An example, I am testing a port from SMF2 and that requires a complete, custom "translation" of the categories, boards and sub-boards (with unlimited nesting level) into the fantastic Tag concept in flarum.
Finally, please do not underestimate that flarum is in beta. API, database schema and much more can change therefore you shouldn't use it in any way, yet, in a production environment. The ideal case is, if you like flarum flavour of forum, to take advantage of this period of developement and install it only to evaluate it/develop your migration script.
These my 2 cents, other might add more details
