The chemical reactions and pathways involving lipids, compounds soluble in an organic solvent but not, or sparingly, in an aqueous solvent. Includes fatty acids; neutral fats, other fatty-acid esters, and soaps; long-chain (fatty) alcohols and waxes; sphingoids and other long-chain bases; glycolipids, phospholipids and sphingolipids; and carotenes, polyprenols, sterols, terpenes and other isoprenoids [goid 6629] [evidence IEA]; The chemical reactions and pathways involving triacylglycerol, any triester of glycerol. The three fatty acid residues may all be the same or differ in any permutation. Triacylglycerols are important components of plant oils, animal fats and animal plasma lipoproteins [goid 6641] [pmid 2833496] [evidence IDA]; The chemical reactions and pathways involving steroids, compounds with a 1,2,cyclopentanoperhydrophenanthrene nucleus [goid 8202] [evidence IEA]; The chemical reactions and pathways involving cholesterol, cholest-5-en-3 beta-ol, the principal sterol of vertebrates and the precursor of many steroids, including bile acids and steroid hormones. It is a component of the plasma membrane lipid bilayer and of plasma lipoproteins and can be found in all animal tissues [goid 8203] [evidence IEA]; The directed movement of phospholipids into, out of, within or between cells. Phospholipids are any lipids containing phosphoric acid as a mono- or diester [goid 15914] [pmid 2833496] [evidence IDA]; The acquisition, loss or modification of a protein or lipid within a very-low-density lipoprotein particle, including the hydrolysis of triglyceride by hepatic lipase or lipoprotein lipase and the subsequent loss of free fatty acid [goid 34372] [pmid 2833496] [evidence IDA]; The acquisition, loss or modification of a protein or lipid within a low-density lipoprotein particle, including the hydrolysis of triglyceride by hepatic lipase, with the subsequent loss of free fatty acid, and the transfer of cholesterol esters from LDL to a triglyceride-rich lipoprotein particle by cholesteryl ester transfer protein (CETP), with the simultaneous transfer of triglyceride to LDL [goid 34374] [pmid 2833496] [evidence IDA]; The acquisition, loss or modification of a protein or lipid within a high-density lipoprotein particle, including the hydrolysis of triglyceride by hepatic lipase, with the subsequent loss of free fatty acid, and the transfer of cholesterol esters from LDL to a triglyceride-rich lipoprotein particle by cholesteryl ester transfer protein (CETP), with the simultaneous transfer of triglyceride to LDL [goid 34375] [pmid 2586614] [evidence IMP]; Any process involved in the maintenance of an internal equilibrium of cholesterol within an organism or cell [goid 42632] [pmid 2586614] [evidence IMP]; The directed movement of periperal cell cholesterol, cholest-5-en-3-beta-ol, towards the liver for catabolism [goid 43691] [evidence IEA]; The chemical reactions and pathways involving phosphatidylcholines, any of a class of glycerophospholipids in which the phosphatidyl group is esterified to the hydroxyl group of choline. They are important constituents of cell membranes [goid 46470] [pmid 2833496] [evidence IDA]; Any process involved in the maintenance of an internal equilibrium of acylglycerol within an organism or cell [goid 55090] [pmid 2833496] [evidence IDA]; Any process involved in the maintenance of an internal equilibrium of phospholipid within an organism or cell [goid 55091] [pmid 2833496] [evidence IDA]