An action is an element that can be added to your survey to perform a task. These tasks are typically performed behind the scenes without the survey respondent being aware of it. There are some though, that are displayed to the survey respondent e.g., ReCaptcha, Results Chart, Review, Social Media etc.
Action Page Compatibility
Actions are not compatible on all pages of a survey. This is typically due to the nature of the action.
For example, if it is meant to collect data (e.g., Hidden Values) it will not be permitted on the Thank You page.
Other actions are used to either present data or notify of a response collected and, thus, only make sense on pages that follow the first page, e.g. Send Email, Result Chart and Review.
Below is a complete list of Action page compatibility.