The discipline of Interaction Design (IxD) concerns the discipline of considering and creating the link between a user and artefacts, e.g. the difference of users using buttons or free text to interact with a bot, or how a cyclist switches gears while racing down a mountain. Interactions can thus take a broad range of components into account, e.g. sounds, speed, colour, motion, social context, aesthetics, time, feedback etc. 

IxD exist every time we use an object, work with a system or utilize and service, and is therefore both physical as well as digital, and the field is thus closely related to UX design, HCI and software design. But since the field is concerned with the “invisible link” between 2 instances (e.g. thing & human) materials, shape, form and physicality are also important, just as affordances, visibility and ease of use are. In the end, however, behaviour in the spectrum between artefact and human is the core, meaning that ultimately context, social systems and psychology take up a big part of interaction designers’ knowledge too.