Form State and Input State

Input fields have the following states:

$untouched The field has not been touched yet.
$touched The field has been touched.
$pristine The field has not been modified yet.
$dirty The field has been modified.
$invalid The field content is not valid.
$valid The field content is valid.

They are all properties of the input field, and are either true or false.

Forms have the following states:

$pristine No fields have been modified yet.
$dirty One or more have been modified.
$invalid The form content is not valid.
$valid The form content is valid.
$submitted The form is submitted.

They are all properties of the form, and are either true or false.