What is the definition or description of: high calcium levels in blood?

Above 10.5 mg/dl. Defining a high level depends on the normal range of the laboratory measuring the calcium level. There is variability. Commonly a high value is greater than 10.5 mg/dl. However some patients may have fluctuating values between normal and high.
Hypercalcemia. Corrected (for albumin) calcium above the upper lot of normal. Causes include sarcoidosis, myeloma, volume depletion and excess calcium intake, cancer, and lots of other things.