Cradle to Cradle is essentially a play on the "Cradle to Grave" phrase, implying that the C2C model is sustainable and considerate of life in general.
Technical nutrients are basically inorganic or synthetic materials manufactured by humans—such as plastics and metals--that can be used many times over without any loss in quality, staying in a continuous cycle.
Biological nutrients and materials are organic materials that can decompose into the natural environment, soil, water, etc. without affecting it in a negative way, providing food for bacteria and microbiological life.
Materials are usually referred to as the building blocks of other materials, such as the dyes used in colouring fibers or rubbers used in the sole of a shoe.
Downcycling is a term used to describe what is conventionally known as recycling, which is seen as "downcycling" materials into lesser products, a plastic computer housing becomes a plastic cup, which then becomes a park bench, eventually becoming waste.
Waste = Food is a basic concept of organic waste materials becoming food for bugs, insects and other small forms of life who can feed on it, decompose it and return it to the natural environment which we then indirectly use for food ourselves.