Return on ad spend (ROAS) is a metric used in the context of online advertising to measure the effectiveness and efficiency of an advertising campaign. ROAS is calculated by dividing the revenue generated by an advertising campaign by the amount spent on the campaign, and is expressed as a percentage. A higher ROAS indicates that an advertising campaign is performing well, and is generating more revenue for every dollar spent, while a lower ROAS indicates that an advertising campaign is not performing as well, and may need to be optimized or improved. ROAS can be an important part of an advertiser's media buying strategy, as it can provide insight into the performance and effectiveness of their advertising efforts, and can help to optimize and improve their campaigns. ROAS can also be beneficial for publishers and platforms, as it can provide insight into the performance and value of their ad inventory, and can help to optimize and grow their relationships with advertisers.