What economic concept would describe how economic recessions and recoveries affect the demand for Dollar Store services?

What economic concept would describe how economic recessions and recoveries affect the demand for Dollar Store services? For this concept, explain how the values might differ for middle-income and lower-income consumers? Explain "The economy's good enough that your middle-income consumers have traded back up, but it's not so good that your lower-income consumers are feeling better." for Dollar Store business.