SSL uses a small portion of labeled data and lots of unlabeled data to train a classification model. There are several methods to label the portion of unlabeled data to be used as a training set e.g. Pseudo-labeling.
Technically, it could be viewed as performing clustering and then labeling the clusters. Unlabeled data within the same cluster as the labeled data share the same label as the labeled data.
https://en.m.wikipedia.org/w/index.php?title=Weak_supervision&diffonly=true
