Reliability measures the consistency of responses. The extent to which someone would answer the same survey with the same answers if taken again would be an example of test-retest reliability. This reliability information is calculated from a survey's internal consistency. We expect people to answer similar items similarly. The extent to which they do is a measure of the survey's internal consistency.
Validity measures the appropriateness of inferences for a test.
The extent to whch people believe the survey is measuring the proper areas. The extent to which the survey actually measures what we intend it to measure. We cannot directly measure it, but we can measure people's attitudes about it. Frequently, the dimension we are measuring is also a construct. Numbers used only for naming.