What is not considered a fixed cost?

Could you please clarify for me what is not considered a fixed cost in the realm of finance and business operations? I understand that fixed costs are those expenses that remain constant and do not vary with changes in production or sales, but I'm curious about what types of expenses are not classified as such. Are variable costs, such as the cost of raw materials or labor that fluctuate with production levels, considered not fixed costs? Or are there other types of expenses that also fall outside of this category?