What is meant by Novgorod's compound engines?

What is meant by calling Novgorod's machinery compound engines?

Compound engines expand steam through multiple stages; here the term identifies an early, relatively inefficient arrangement rather than a mature double- or triple-expansion engine.

Compound machinery uses more than one stage of steam expansion and generally works more efficiently than a single-expansion engine. In this explanation, the word distinguishes an early, comparatively inefficient arrangement from machinery described more specifically as double or triple expansion. Novgorod's engines were horizontal compound-expansion engines built by Baird Works in St Petersburg. The builder's Scottish founder explains the British industrial connection, despite an initial mistaken reference to the works being in Scotland.