Omnichannel support is customer service that handles every channel a customer uses, such as email, chat and social messages, in one place with one shared history per customer.
Multichannel just means you are on several channels. Omnichannel means they are joined up: if a customer messages on Instagram and then emails, the person answering sees both, and the customer does not have to repeat themselves.
For most small shops the channels that matter are email, live chat on the site, Instagram and Facebook Messenger, and the contact form. Answering all of them from separate apps is how messages get missed.
Hobson brings email, live chat, Instagram, Messenger and contact forms into one inbox, and drafts a reply on each with the Shopify order beside it. See all channels.