In the definition of SSO, you have an identity provider and multiple resources that uses this central identity provider to authenticate users so they only ever need to have an account at the central identity provider instead of separate accounts for the underlying resources.
Socialite provides a solution for your users to authenticate themselves to your website using a third party website (integration). In that sense, Socialite provides SSO for your Laravel application, as users can use their central identity provider of choice (for example Google, Github, Twitter, etc.).
Additionally, socialite also provides an integration with Laravel passport if you want to use your own website as a central identity provider (instead of Google, Twitter, etc.). If you're interested in setting that up, I wrote a blog post on that topic a little while ago: https://johnbraun.blog/posts/oauth2-authentication-across-laravel-projects