How to display string that contains HTML in twig template?

Question

Use raw keyword, http://twig.sensiolabs.org/doc/api.html#escaper-extension

{{ word | raw }}

You can also use:

{{ word|striptags('<b>')|raw }}

so that only <b> tag will be allowed.

{{ word|striptags('<b>,<a>,<pre>')|raw }}

if you want to allow multiple tags

if you don't need variable, you can define text in
translations/messages.en.yaml :
CiteExampleHtmlCode: "<b> my static text </b>"

then use it with twig:
templates/about/index.html.twig
… {{ 'CiteExampleHtmlCode' }}
or if you need multilangages like me:
… {{ 'CiteExampleHtmlCode' | trans }}

Let's have a look of https://symfony.com/doc/current/translation.html for more information about translations use.