A web 2.0 backlink is simply a HTML link from a website, which is considered a web 2.0 property. Web 2.0 are 3rd party blogs which allows you to make blog on their website and make backlinks for your website. It gives boost to ranking of your website. You can create blog as many as you want and also you can make backlinks according to your requirements.
Web 2.0 properties are sites where anyone can create a free blog on the domain, and hence they can write content on the platform and post links.
WordPress, Tumblr, Weebly, Blogger, Jimdo, etc are examples of these domains.
The advantage of gaining backlinks from web 2.0 platforms is that they are considered trustworthy by Google, as they have a high Domain Authority (An SEO metric that Moz use to indicate how powerful a website is).
Therefore, gaining a link from web 2.0 platforms is definitely worth it, but it can take a while to setup these sites, create content and link out.
They give you all the login details too, so you can add more content, or make edits as you please.
I started a new website in early March 2019, and after 5 months of just using the following web 2.0 service on SEOClerks, my site is now ranking very well for low & medium competition keyword terms.
I hope that you find this helpful. And to all of those who may say web 2.0 links do not work anymore… My tests and the case study above says otherwise 🙂