Concentration or density of a substance in a solution or mixture (e.g., salt concentration, alcohol concentration) — used in chemistry and everyday contexts.
血液の糖濃度を測定するために検査を受けた。
I underwent a test to measure the glucose concentration in my blood.
溶液の濃度を正確に希釈して調整する必要がある。
It's necessary to accurately dilute and adjust the concentration of the solution.
In mathematics, '濃度' can be used in specialized contexts to refer to cardinality or a measure of the size/density of a set (a technical usage).
無限集合の濃度（基数）について講義を受けた。
I attended a lecture on the cardinality (濃度) of infinite sets.