Canonical URL
A canonical URL tells search engines which version of a page is the preferred one when similar content exists at multiple URLs (trailing slash variants, query parameters, http vs https, www vs apex). Set via <link rel="canonical" href="..." /> in the <head>. Missing canonicals are a top cause of "duplicate content" issues that split link equity and suppress rankings.
한국어
Canonical URL은 비슷한 콘텐츠가 여러 URL에 있을 때(trailing slash, 쿼리 파라미터, http/https, www/apex) 검색엔진에 선호 버전을 알려줘요. <head>에 <link rel="canonical" href="..." />. 누락 시 중복 콘텐츠 문제로 링크 에쿼티가 분산되고 순위가 떨어져요.
日本語
canonical URLは、似たコンテンツが複数URL（末尾スラッシュ、クエリ、http/https、www/裸ドメイン）にあるとき、検索エンジンに優先版を伝えるためのタグ。<head>に<link rel="canonical" href="..." />。欠如は重複コンテンツ問題とリンクエクイティ分散の主因。