Anchor text is the clickable text portion of an HTML link (<a> tag). In "<a href='...'>this text</a>," "this text" is the anchor text.
Anchor text is a key signal search engines use to understand the linked page's content. A page linked with the anchor text "how to use shortened URLs" is recognized by Google as relevant to the keywords "shortened URLs" and "how to use."
There are six main types of anchor text: exact match (the target keyword itself), partial match (a natural phrase containing the keyword), branded (site or company name), naked URL (https://example.com), generic ("click here," "learn more"), and image link (the image's alt text serves as anchor text).
A key consideration with shortened URLs and anchor text: pasting a shortened URL as plain text makes the anchor text a meaningless string like "https://miji.be/abc123." From an SEO standpoint, even when using shortened URLs, wrapping them in an HTML link with meaningful anchor text is preferable.
The main pitfall in anchor text optimization is overusing the same keyword. Since Google's Penguin update, unnatural anchor text patterns are flagged as spam. A natural link profile contains a balanced mix of branded, naked URL, generic, and keyword-containing anchor texts. You can find related books on Amazon.