Proactive linkbuilding (blogger outreach and link negotiation etc) is the main form of outbound marketing in SEO. Meanwhile, all on-site work is a form of inbound marketing.
Inbound marketing in SEO
Pretty much all on-site SEO work is a form of inbound marketing. Let’s look at some key examples.
Outbound marketing in SEO
Linkbuilding strategies that involve outreaching to relevant publishers, to negotiate them linking to your site or working with you to help attract links from other parties, is a classic example of outbound marketing in SEO.
Link negotiation can involve anything from offering free merchandise to social media influencers in order to encourage them to review your products and link to you in the process, through to creating articles specifically for bloggers to publish on their blogs, with ready-made links built into those pre-written articles (as in common in guestposting).
Suggesting link exchanges, where you would publish a link on your site pointing to someone else’s site in exchange for them publishing a link on their site pointing to your site (a reciprocal link exchange deal), is still a popular type of linkbuilding outreach, albeit quite dated. Note that link exchanging with lots of sites is discouraged by and very easily detected by search engines, thus link exchange deals are best constructed in a non-circular (linear) 3-way manner and even then you should question your ethics else risk the wrath of Google penalties in case your scheme is somehow detected!