Sensitivity is the proportion of truly diseased persons in the screened population who are identified as diseased by the screening test (i.e. they have high scores).  Sensitivity indicates the probability that the test will correctly diagnose a case, or the probability that any given case will be identified by the test.  

To help you remember the term, being sensitive implies being able to react to something.
Specificity is the proportion of persons without the disease who have low scores on the screening test: the probability that the test will correctly identify a non-diseased person.  To help you remember the term, a specific test is one that picks up only the disease in question, so it has a narrow focus, which explains the term 'specific'. 
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