Using TinyMCE, it is possible to define HTML tables with a caption.

Ref:
https://doc.ez.no/eZ-Publish/User-manual/5.x/The-Online-Editor/Usage/The-toolbar#Working-with-tables
http://www.w3schools.com/tags/tag_caption.asp

If the frontend siteaccess is in legacy mode, the table caption will be displayed. However, if it is in new stack mode, it will NOT be displayed. Please make sure it is.

Steps to verify this:

• Prepare test installation, and ensure the "eng" frontend siteaccess is in new stack mode (it is, by default);
• Go to the admin siteaccess;
• Create an article;
• On the "body" field, click the "Insert a new table", and fill in the details, a specify a caption (e.g. "Test caption");
• Publish;
• With "eng" SA in legacy mode: the table caption is displayed, as expected;
• With "eng" SA in new stack mode: the table caption is NOT displayed.