What is the difference between a gezeiroh and a shvus?
Both a shvus and a gezeira are m’drabonon, the difference between them is that a shvus is derived from the verse Shemos 23-12 “u’byom hasheve’ei tisbos”, and it is specifically regarding shabbos. Usually chazal did not make a geziero on top of another gezeiro, however regarding sevusim, which are more severe, they made a fence around a fence around another fence, in order to preserve the sanctity of shabbos. For example, chazal forbade doing commerce on shabbos as a shvus that we shouldn’t come to write a receipt. They further forbade reading receipts, and they even forbade reading other material because it would be similar to reading business material.