Polyunsaturated Fat (PUFA) has more than one double bond. PUFA are liquids even when ice cold. Animals cannot make PUFA. PUFA are very vulnerable to oxidation because of the multiple double bonds. There are two classes of PUFA, depending on the location of the first double bond: omega-6 (n6) and omega-3 9(n3).
The most common omega-6 PUFA is linoleic acid found in soybean and corn oil. which has 2 double bonds. Linoleic acid accumulates in non-ruminant animals if you feed them corn and soybeans. Linoleic acid is turned to archidonic acid by an enzyme called D6D. Oxidized linoleic acid metabolites (OXLAMs) activate PPAR gamma.
Omega-3 PUFA include alpha-linolenic acid (ALA) in flaxseed oil, which has three double bonds. EPA and DHA from fish oil are longer, highly unsaturated n3 PUFA.