What is the difference between on-page, off-page and technical SEO?

• Technical SEO — making the site crawlable, indexable, and fast. Site architecture, robots.txt, XML sitemaps, canonical tags, redirects, structured data, HTTPS, mobile-friendliness, Core Web Vitals, and JavaScript rendering. It is the foundation: without it, nothing else can work.
• On-page SEO — optimising the content and HTML of individual pages. Search intent matching, content quality and depth, title tags and meta descriptions, heading structure, internal linking, image alt text, and URL structure. This is where you have the most direct control.
• Off-page SEO — signals from elsewhere, principally backlinks from other sites, which remain among the strongest ranking factors. Also brand mentions, digital PR, and for local businesses the Google Business Profile and citations.

How they relate: technical SEO is necessary but not sufficient — a perfectly crawlable site with poor content ranks for nothing. On-page is where most sites have the largest unexploited opportunity. Off-page is the hardest to influence and the hardest for competitors to replicate, which is why it carries weight.

Note: The right prioritisation to state: fix technical blockers first because they cap everything else, then on-page because it is within your control, then off-page because it is slow and expensive. Investing in link building while pages carry noindex tags is a real and common mistake.