Final answer:
Repression is the primary unconscious defense mechanism that prevents intense, anxiety-producing thoughts or memories from reaching conscious awareness, acting as a mental block against distress.
Step-by-step explanation:
The term that refers to the primary unconscious defense mechanism that keeps intense, anxiety-producing situations out of a person's conscious awareness is repression. Repression acts like a mental block, preventing overwhelming and potentially distressful memories or feelings from entering one's conscious mind.
To illustrate, if an individual has a memory that is too traumatic, the mind may automatically suppress it to protect the individual from psychological distress, akin to turning up the radio to ignore the unsettling noise of a malfunctioning car, as the memory fades from conscious thought.