Omnichannel is a term used to define a web presence of a brand on every possible sales channel or platform that is possible for sales in an industry. The term mostly relates to the marketing industry where marketers are tasked to create the presence of the brand on every platform and when they accomplish that, it is called omnichannel marketing.
For the e-commerce or printing industry, this term can also mean registering your product on every possible platform that sells its product and caters to the audience from their category. Right from marketplace platforms like Amazon, and eBay to having a brand-personalized website and mobile application to registering on social media platforms and online shops, every platform has to be covered to create an omnipresence of a brand.