Embodied carbon is a measure of the amount of carbon dioxide produced in the creation of a material. It encompasses the entire path from raw material production to final product manufacturing. For metals, the value is a composite of virgin and recycled values, weighted by average global recycling percent. The virgin material value starts at ore extraction, and is higher than the recycled value.
Embodied carbon values often correlate with embodied energy values. The main difference comes from different carbon footprints of different energy sources. Unfortunately, this makes the values sensitive to both geography and time. The carbon footprint of a unit of energy tends to shrink over time (as, for example, coal is phased out in favour of other sources), but finding what year a particular value in the literature comes from can be surprisingly challenging.