Field-level theming determines how the values of a given field are displayed. The resulting output ends up in the $content and $<FIELD_NAME>_rendered variables in the node templates.

Template files

In order to customize field themeing:

Template suggestions

In addition, the theme layer will also look for field-specific variants (suggestions), in the following order of precedence:

content-field-<FIELD_NAME>-<CONTENT_TYPE_NAME>.tpl.php
ex: content-field-field_myfield-story.tpl.php - If present, will be used to theme the 'field_myfield' field when displaying a 'story' node.
content-field-<CONTENT_TYPE_NAME>.tpl.php
ex: content-field-story.tpl.php - If present, will be used to theme all fields of 'story' nodes.
content-field-<FIELD_NAME>.tpl.php
ex: content-field-field_myfield.tpl.php - If present, will be used to theme all 'field_myfield' field in all the content types it appears in.
content-field.tpl.php
If none of the above is present, the base template will be used.
Important:

See the Working with template suggestions section of the Theme guide for Drupal 6 for more informations about templates and template suggestions.