Beside the raw wiki content, DokuWiki stores useful information, like title, backlinks, date of last edit etc. as metadata for each page. This data follows the Dublin Core Standard for metadata.

• The title of your page is stored within metadata files, if you see the ID of your page instead of the full title, see the useheading option.

• Metadata can be used to customize your templates via tpl_pageinfo or tpl_pagetitle for example.
• For deeper use of metadatas, you can also look at p_get_metadata and p_set_metadata.
• For resources on how this metadata can be used/accessed for plugin or template development please refer to the development page.

• More reference here : losing all meta data.
  According to HansBKK experience, losing all meta data might not have any actually impact of losing any data (data/pages/) (but metadata used by plugins will lost however), and new metadata can be regenerate by bin/indexer.php. Do any people can improve this answer? I'm curious too :) — treegb 2016-10-09.