block
is a Twig function to print a block multiple times when a template uses inheritance.
<title>{% block title %}{% endblock %}</title>
<h1>{{ block('title') }}</h1>
{% block body %}{% endblock %}
The block function can also be used to display one block from another template:
{{ block("title", "common_blocks.twig") }}
Use the defined test to check if a block exists in the context of the current template:
{% if block("footer") is defined %}
...
{% endif %}
{% if block("footer", "common_blocks.twig") is defined %}
...
{% endif %}
See also
Source: [Twig](https://twig.symfony.com/block)