My definition: there is no clear limit, but there is a spectrum of ‘roboticity’ that corresponds to the spectrum of ‘versatility’. The more versatile a machine is, the more a robot it is.

For instance, a blender is not versatile. But a cooking robot can do more things (it blends, but also cooks, mixes, etc.). This is why the cooking robot is more a robot than a blender.

This is similar in industry. You have specialized machines, which can do a single thing. Industrial robots are more versatile because we can program them to achieve different task (e.g. when there is a new model of car). The ultimate robot would be as versatile as a human. This kind of humanoid would have the highest level of ‘roboticity’.