correlation and causation

Question 1

what is correlation

Answer 1

when there is a statistical relationship between two things but how that relationship works is unclear/unknown

Question 2

what is bidirectional ambiguity?

Answer 2

when there is a correlation between two things but it is unclear in which direction the relationship runs

Question 3

what is a 3rd lurking variable?

Answer 3

when there is a third variable connected to both things - eating more ice cream causes more drowning in summer pools - lurking variable is nice weather