Why doesn't jQuery work on wordpress?

Question

CMS

There is a site on wordpress medcentr-iz.com.ua . On the main page, there is a script that, on low extensions, opens the side menu when the button is clicked. But on other pages, the same script does not work, like other jQuery scripts. What could be the problem?
the script itself
jQuery(document).ready(function(){
jQuery('nav .nav_mob img').click(function(){
jQuery('.navigation').hide(1000);
jQuery('.navigation_mob'). show(700);
})
jQuery('.nav_mob_title .close').click(function(){
jQuery('.navigation').show(700);
jQuery('.navigation_mob').hide(300);
} )
})

Answer 1

Because jQuery is not included:

Uncaught ReferenceError: jQuery is not defined

Answer 2

thanks, it helped. Although it is strange that the main page worked without including jquery. The script is the same