Reliability:This refers to the consistency of a research study or measuring test. For example, if that same weighing scale gives you different readings every time you step on it, then it lacks reliability.
Construct Validity: This type of validity ensures that the measure of a variable actually measures the construct it is designed to measure. For instance, if an intelligence test measures intelligence and not something else (like memory), then we can say this test has construct validity.
Content Validity: This refers to how well a test measures all aspects of a given social concept. For example, if an exam covers all topics taught in an AP Psychology course rather than just one topic, then this exam has content validity.