What type of fee structure is described as an honorarium plus reimbursable expenses?

The fee structure that is described as an honorarium plus reimbursable expenses typically refers to a model where a professional is compensated not just for their time but also for expenses incurred during the course of their work. An honorarium is a payment given for professional services that are rendered nominally without charge. Combining this with reimbursable expenses means that while the professional receives a base amount for their expertise or contribution (the honorarium), they can also claim costs associated with performing their duties, such as travel or materials.

In this case, a per diem is a relevant choice because it often serves as a daily allowance for expenses incurred while performing work-related tasks. Providing a flat amount plus coverage for additional expenses aligns well with this definition. This flexibility allows for variations in costs while still providing the professional with guaranteed compensation for their time and contribution.

Other fee structures, such as hourly fees, retainers, and fixed fees, do not adequately capture the combination of a base payment for services rendered alongside reimbursable costs in the same manner. Each has distinct characteristics that do not fit the description provided in the question.