The phrase "upper limit" refers to the highest or maximum value that something can reach or go up to. It sets a boundary or restriction indicating that there is a point beyond which no further increase or advancement is possible. Full definition
How come we can accept variations on upper limits of blood pressure, heart rates, body fat, cholesterol, etc., but not blood glucose? (freetheanimal.com)
It's possible that may be placing some kind of upper limit on my actual reading speed. (makingitupasigo.com)
Based on the assessment that reserve data may be taken as upper limit for practically relevant coal quantities to be produced in the future, production profiles are developed. (resilience.org)