The description is mangled...

"Spec is a list of terms, where each element is one of."

Found it very hard to grok without an example. Here is one: =https://swish.swi-prolog.org/p/order_by%20example.swinb=[Your text to link here...](https://swish.swi-prolog.org/p/order_by%20example.swinb)

data(0, 1, 1).
data(1, 0, 0).
data(0, 0, 0).
data(1, 2, 0).
data(1, 0, 1).
data(0, 2, -1).
data(1, 1, 1).
data(0, 1, 0).

?- order_by([desc(B),asc(C)], data(A,B,C)).

A = 0, B = 2, C = -1  ;
...

For more see: Your text to link here...