Why $ for jquery doesn’t work?

I used the following to enqueue jquery plugins:

<?php
    function my_scripts_method() {
        wp_enqueue_script(
            'custom functions',
            get_template_directory_uri() . '/js/main.js',
            array('jquery'),
            '1',
            true
        );
        wp_enqueue_script(
            'dotdotdot & lightbox',
            get_template_directory_uri() . '/js/plugins.js',
            array('jquery'),
            '1',
            true
        );
    }
    add_action('wp_enqueue_scripts', 'my_scripts_method');

And I don’t know it it’s related but jquery only responds to calling jquery(... and not $(.... Why is that?