Flexible expenses mean expenses that can be easily altered by the person or institution bearing the cost.
In personal finance, these kind of expenses include luxury items, clothes, entertainment, or vacation while house mortgages or car payments are fixed expenses.
Business flexible expenses include for example training, hiring outsourced help, business card printing, website development and entertainment of clients. These expenses can be changed whenever the company is low on money or needs something specifically. On the other hand, wages for employees, rent for the office space, electrical and utility bills, Internet and telephone services are considered as fixed expenses.
In certain circumstances, necessary expenses can be considered flexible if the company needs to cut back on them. For example, the firm may move to a less expensive office.