Set or alter the page title
You can override the page title or append/prepend text to it.
Set the page title
_page.title = 'New Title' %}
Append text to the existing page title
{% set _page.title = _page.title ~ ' New title'%}
Prepend text to the existing page title
{% set _page.title = 'New title ' ~ _page.title %}
Example scenario
One scenario would be to add the pagination page number to the title when someone is navigating through a paginated list of content.
{% if pagination.current > 1 %}
{% set _page.title = _page.title ~ ' - Page ' ~ pagination.current %}
{% endif %}