In correlational research, the description is of the relationship between

Correlational research describes the relationship between interval variables measured on continuous scales.

Interval-level data allow meaningful correlation coefficients to be computed.

Nominal variables only classify and cannot enter a standard correlation directly.

Intervening variables lie within the causal chain and are not what correlation describes.

Chance variables is not a recognised variable type here.

Pearson's r is the common measure for such interval associations.