Learn in the textbookAttacks on Web Applications
DefinitionClickjacking (クリックジャッキング) is an attack that lays another site's page, made transparent, over a trap page so that the user clicks a button they never meant to press.
ExplanationThe user sees only the trap page's buttons, but the button they actually press belongs to the invisible page on top. As a result, in a service the user is logged in to, settings get changed or who can see the user's content gets switched without the user knowing. One countermeasure is a setting that stops the site's own pages from being displayed inside other sites.
AnalogyIt is like standing a clear panel with its own switch in front of a sign's button, so that anyone reaching for the sign's button presses the panel's switch instead.
Memory hookThe "jacking" is the same "jack" as in hijack. What gets hijacked is the user's click.