Pseudo-cleft

In the pseudo-cleft construction, like the cleft construction, some part X of a sentence is focussed.

Example
(ii) is a pseudo-cleft version of (i). The focussed part X (a herring) is associated with a free relative clause in a copula construction:

(i) John ate a herring (ii) [What John ate e] was a herring

Links
Utrecht Lexicon of Linguistics