Variables in module using colons I think this may be related to using "tokens" when developing a module, but I am seeing this:

'og:updated_time' =&gt; array('value' =&gt; '[node:changed:custom:c]'),


The question I have is about:  [node:changed:custom:c] 

What is this? What is it even called? 

In my particular case, I am adjusting a module to retrieve a new value from a custom field.

'og:image' =&gt; array('value' =&gt; '[node:field_social_image]')


I have successfully used this for other custom fields, using the exact same syntax, but this one does not work.
These are the tokens, more specific a custom/dynamic tokens implemented by Drupal core (token.inc) and managed by Token module.

See: List of tokens page for more details:


  Custom format [node:changed:custom:?]   "?" is a single, unquoted PHP date formatting character. Use this token multiple times to build a full custom format.