A link wheel is snake oil SEO. Confusing hogwash that feigns to be the magic bullet.
A link wheel is, for example when you have 6 sites: A B C D E F. If A is your main site, then B, C, D, E, F link to A reciprocally. Then B links to C, C links to D, D links to E, E links to F, and F links to B completing the wheel. This is the basic variant.
A link wheel is not a killer SEO tactic, at least not anymore. Check the dates on the posts that mention it: 2006, 2005, 2007. SEO, or at least "killer" SEO tactics, are outdated fast. Proper SEO:
Content is king
Make your content accessible
Get backlinks
never changed.