Final answer:
The subject of this question is Social Studies. The term 'this' refers to the share of household income that is given to certain expenses or saved for future use.
Step-by-step explanation:
The subject of this question is Social Studies. In the context of the provided information, the term 'this' refers to the share of household income that is given to certain expenses or saved for future use. It is mentioned that households give less than 1% of their income to 'this'.