Big data refers to the large and complex data sets that are difficult to analyze using traditional data processing applications. In digital marketing, big data can provide insights about customers from various sources like transactions, locations, surveys and social media. It can help determine what influences customer loyalty and optimize marketing spends across channels. The biggest challenges of big data in marketing are knowing what data to collect, which analytical tools to use, and how to translate data into meaningful insights. Common digital marketing tools that utilize big data include display advertising, search engine marketing, social media marketing and analytics platforms.