"covariance" - key terms from Wikipedia

covariance
covariance and contravariance
covariance and contravariance of vectors
covariance function
covariance group
covariance matrices
covariance matrix
covariance matrix c
covariance structure of the errors
eddy covariance
error covariance
estimate covariance
general covariance
mean and covariance
measurement covariance
pca using the covariance method
posterior error covariance
state and covariance