What is the purpose of an siRNA screen in drug discovery?
According to the Labome article &quot;siRNAs and shRNAs: Tools for Protein Knockdown by Gene Silencing&quot; siRNA does stand for small interfering RNA.
siRNA is used to silence genes via mRNA degredation:

NA interference (RNAi) is the process by which the expression of a target gene is effectively silenced or knocked down by the selective inactivation of its corresponding mRNA
[...]
The silencing mechanisms can either lead to the degradation of a target mRNA, as induced by small interfering RNAs (siRNAs) or short hairpin RNAs (shRNAs), or the suppression of translation of specific mRNAs, as induced by microRNA (miRNA).

There are also Wikipedia articles discussing these concepts that didn't come up in my search somehow, but a colleague linked me to:

Gene knockdown
Small interfering RNAs