Turmeric is a spice which contains curcumin. As with all spices, concentrations vary based on variety, growing conditions, storage, any fillers used... Curcumin is the active ingredient extracted from the turmeric, and can be measured exactly. Kind of like marijuana, which contains both CBD and THC - only in the raw, you don't know how much of each, or what else is in it.
The healing properties of curcumin and some other substances can be difficult for the body to extract, leading most of it to be immediately excreted in urine. This article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6770259/ explains some of the mechanisms tested to cause more absorption of curcumin.