A clinical study is established to determine if the results of a screening stress test can be used as a predictor of the presence of heart disease. The study enrolls 100 participants who undergo a screening stress test and then have their disease state confirmed by an angiogram (gold standard). Twenty participants screened positive with their stress tests and had confirmed heart disease on their angiogram. One participant who screened positive on his stress test had a normal angiogram and did not have heart disease. Seventy-seven participants screened negative on their stress tests and had normal angiograms without heart disease.

What is the specificity of the screening stress test? What does this mean in nonstatistical language, or plain English?