Who is referred to as a "spendthrift"?

A "spendthrift" is a term used to describe someone who spends money extravagantly and wastefully, often without regard for budgeting or saving. This concept emphasizes a lack of financial prudence, where the individual may indulge in impulsive buying or overspending on luxuries.

The definition aligns with the answer that identifies a spendthrift as someone who spends money prodigally, meaning they are very generous or extravagant in their expenditures, which can often lead to financial difficulties.

The other options highlight behaviors associated with saving, investing, or budgeting, which contrast sharply with the traits of a spendthrift. A spendthrift does not save diligently, invest wisely, or calculate expenses carefully, as those actions involve a level of fiscal responsibility and planning that is not characteristic of a spendthrift's behavior.