What does fixed monthly cost mean?

Excuse me, could you please clarify what you mean by "fixed monthly cost"? I understand that it refers to an expense that remains constant each month, but are there any specific contexts or industries where this term is commonly used? For example, does it apply to subscription-based services, rent payments, or utility bills? Additionally, is there a way to determine if a particular cost is considered fixed or variable, and what factors might influence this classification? Thank you for your assistance.