Is it possible to combine contextual filters with regular filters?
You can add "or" conditions to filters -- either regular or exposed -- using Views in Drupal 7 or 8 (in Drupal 6 you need to use the Views Or module). 

Add the filters you want -- in your example, a "Has taxonomy term" filter for "meta" and a "Has taxonomy term" exposed filter. Then click the arrow next to the "Add" link to expand the options and select "And/Or, Rearrange".



From there you can add a new group and drag both the "Has taxonomy term" filters into that group and set the operator to "or". (You can also set the operator between groups to "or" for more complicated scenarios.)



To add OR clauses to contextual filters, tick the "Allow multiple values" option and use the "+" or "," characters in the URL to indicate an OR or AND of values.

That should get you what you want.