WordPress Site Title is the Title given to the website.
The tagline is something like a slogan, subtitle which tells the visitor what is on the website or article. It simply gives a better idea of what the visitor will see on that.
So be careful while giving a tagline as it reflects the SEO too.
Here’s how to echo or print a title or tagline in the template using PHP:
For the website name:
<?php echo get_bloginfo('name'); ?>
For the tagline:
<?php echo get_bloginfo('description'); ?>