Yes, it's often defined in language file:
/language/en-GB/mod_footer.ini
MOD_FOOTER_LINE1="Copyright © %date% %sitename%. All Rights Reserved." ; Note : %date% will be auto replaced by current year! Don't translate
MOD_FOOTER_LINE2="<a href=\"https://www.joomla.org\">Joomla!</a> is Free Software released under the <a href=\"https://www.gnu.org/licenses/gpl-2.0.html\">GNU General Public License.</a>"
MOD_FOOTER_XML_DESCRIPTION="This module shows the Joomla! copyright information."
To override, you can simply go to Backend >> Language Overrides >> and override language constants:
MOD_FOOTER_LINE1
MOD_FOOTER_LINE2