Click-through rate (CTR)
Click-through rate says how many people clicked your search result, measured against everyone who saw it. A hundred impressions and three clicks make three per cent.
It is the one search metric you can influence directly without changing your position: the title and description decide whether someone clicks. A page in fourth place with a good title regularly beats one in third with a poor one.
The value depends heavily on position and even more on the kind of query. Someone looking for a phone number often gets it in the result itself and never clicks — which pushes the rate down without anything being wrong.
So click-through rate is always read in relation, never on its own: against your own position, your own history and the type of query. A low rate on a question the search engine answers itself is not a shortcoming.