strip_tags

"<b>Fish</b> & <script>alert(1)</script>Chips"

Removes all tags, keeping only their content as text (the content of <script> is kept too). The returned string is already escaped (& becomes &, " becomes ", ' becomes ', etc.), leaving already escaped parts such as & as is (though a character reference such as © may be turned back into its character), and marked as html_safe, so <%= %> does not escape it again.