My (admittedly, very layman) understanding is that prions are proteins that are misfolded in such a way that when in proximity or contact with their 'correctly

My (admittedly, very layman) understanding is that prions are proteins that are misfolded in such a way that when in proximity or contact with their 'correctly folded' version can induce them to change shape to the misfolded version. Prions are below the level of things like viruses or bacteria -- they are a result of the underlying chemistry of making proteins. Proteins and their folding is arranging atoms into energetically favorable states. A prion is then a different arrangement of the atoms that is somewhat more energetically favorable, one that can induce other proteins to transition to this different state. It is this last property that makes them infectious.