A Passthrough is a cost in a video budget that does not get marked up with a production fee, but gets passed on at cost. At cost often means that a 10% service fee is added, to cover accounting, insurance, and administration on the cost, but it’s not meant to be an income stream for the production company. Typical passthrough items are: travel related costs, meals, per diems, and local transport.
Ironically, budgets today are so tight, that there’s nary a difference between a mark up and a passthrough.