Also called omnichannel, multichannel selling, unified commerce
Omnichannel retail means a customer can buy from you in several ways, and the shop treats them as one business. The counter, phone orders, WhatsApp, your website and marketplaces all draw from the same stock and land in the same order list.
The common problem with selling in many places is overselling. If the website shows 5 units and the counter sells 4 before the website knows, an online customer orders something that is not there. The fix is a single stock count that every channel sells from, with a buffer kept for the counter.
A shop has 20 units of a pressure cooker. It allows 8 on a marketplace, 6 on its own website and keeps 6 for walk-in customers. Kownt X draws its own storefront and marketplace channels from the same inventory, with allocations and buffers per channel.