Technical SEO includes the parts of SEO that affect how search engines access, crawl, index and understand your website.
This can include website crawlability, indexation, sitemap setup, robots.txt, redirects, broken links, canonical tags, duplicate content, schema markup, internal linking, URL structure, page speed, mobile usability and Core Web Vitals.
For WordPress websites, technical SEO can also involve fixing issues caused by plugins, page builders, old redirects, thin category pages, missing metadata and messy templates.