Found:

cleft

SYNTAX: a Cleft construction can be derived from a non-cleft construction by introducing one of its elements, say X, in a clause having the form It be X, and by turning the rest into a relative clause. Two cleft versions of (i) are given in (ii):

(i)    We saw John
(ii) a It was John [who we saw e]
     b It was John [that we saw e]