How do you pull entries with a specific category value? Help, I forgot how to do something basic. 

How do I pull all the entries in posts for a specific category value (field name = countryName) within the category group called country?   

And I am NOT using the template for posts or the category.

I can pull all the entries using 

{% for doc in craft.entries.section('posts') %}
--OR-- 

{% set entries = craft.entries.section('posts') %}

But, I forgot how to now add a second condition to pull up only those entries with the countryName (say) "United Kingdom"?

Thank you.
Is this the best way to do it?

`{% set results = craft.entries.section(posts).search('countryName:"United Kingdom"') %}


It appears to work.