Possible values: an array of values to exclude, or a string specifying a single value to exclude
This parameter allows you to exclude specific options from select, multi-select, checkbox and radio button fields. This is useful if you need to exclude certain option(s) from a field that generates its options automatically (such as a taxonomy field).
You can pass in a single value to exclude:
'exclude' => 'some-category'
Or an array containing multiple values to exclude:
'exclude' => array('some-category', 'another-category')
Note: This parameter expects to receive the VALUES of the options to exclude, not their labels. This means that the actual value of a particular option may not be the same as what appears to the user. For instance:
<option value="this-is-the-value">This is the label</option>
This parameter is only valid with select, multi-select, checkbox and radio button fields.