What does it mean to be mildly positive to ischemia?

Some ischemia: Don't ever hesitate to ask your doctor to explain a term used during your visit! in general mild ischemia means that there is some documented reduction (inadequate) in the normal flow of blood, i.e. Ischemia. I don't know what kind of test you had or if you are referring to your heart or some other part of your body. Without more information i cannot be more specific.

Test positive: Stress testing is a functional cardiac test for coronary disease treadmill, dipyridamole, or other stressors are used to elevate heart rate and oxygen need. If ekg or echo or nuclear changes are identified that signifies stress ischemia and a positive test. That usually means a heart catheterization is coming.

Blocked artery maybe: I'm assuming that this refers to the result of a stress test in answering this question. Ischemia means that part of the heart is not getting sufficient blood flow. The mildly positive part of the result suggests that the interpreting doctor thought that either the area of the heart involved is small, or the degree of abnormality seen on the test was small. This could be due to a narrowed artery.

Arterial blockage.: Ischemia in areas of the heart, as you have related, infers that the arteries that feed these parts of the heart are narrowed such that blood flow through them reduces with exertion. It means these areas of the heart are vulnerable and further testing is needed and intervention may be necessary.