It refers to the process of optimizing your website. And there a lot of great practices of technical SEO: optimize URL structure, navigation and website structure, website speed, etc.
So technical SEO consists of a number of checks and settings you need to optimize to help search engines crawl and index your website without any problems.
Technical SEO is the process of ensuring that a website meets the technical requirements of modern search engines with the goal of improved organic rankings. Important elements of Technical SEO include crawling, indexing, rendering, and website architecture.
Technical SEO is basically optimizing your site for speed and performance. It is also sometimes related to website design. Technical SEO is basically done to improve user experience and user interface by creating easy navigation, higher website loading speed, visually appealing webs design, etc.