Budget and bid optimisation is the ongoing adjustment of how much you spend and how much you bid in paid campaigns to maximise return. It covers shifting budget towards campaigns, audiences and products with better ROAS or margin, and choosing bidding strategies such as target ROAS, target CPA or maximise conversion value.
For eCommerce, the goal should be profit, not only revenue. Feeding margin data into the platforms leads to better decisions than optimising for sales alone.