Final answer:
Housing cost-burdened is a measure of relative poverty where a family or individual spends more than 30% of their income on mortgage or rent. Therefore, the correct option is a) relative poverty.
Step-by-step explanation:
When more than 30% of a family's income goes to a mortgage or rent, they are considered housing cost-burdened. This is a measure of relative poverty. Relative poverty refers to the economic condition where a family or individual has a lower income than the average median income, making it difficult to meet the average standard of living in society.