Conversion in ux design
Initially in terms of e-commerce ux design, conversion is the index showing how many visitors actually moved to the end of the way they were offered actually buying a product. So, for e-commerce conversion transforms visitors (users) into buyers.
Today ecommerce uses wide range of techniques, so in terms of web or app platforms meaning of conversion also gets broader.
In modern terms of improving user experience ,comprehensive and numerous functions and needs, which users are able to fulfill with online resources and digital products, conversion is the rate of cases when visitors did the action they were called to. And that can be not only buying something.