In few decades ago, marketing collateral referred primarily to printed material such as brochures and flyers. Today it involves a huge collection of online and offline media, used both to support the sales process and inform viewers about the services and products a particular business offers. Every piece of content, illustration, video, social media post, etc. can be considered as marketing collateral. Basically, it can be anything that tells customers who you are, and what you do. Marketing collateral is usually used after initial contact with customers through advertising or other means, often running parallel to the company's primary advertisement scheme.
A good marketing collateral visually reflects your company's corporate identity and is written in a consistent tone. It should be made keeping the customers in mind, aimed to solve their problems or queries when buying a product or service. Having a strong collateral marketing strategy has many benefits such as carries your brand in such a way that brings you closer to your customers, with competitive materials that is constantly evolving, diversifying, and developing.