- A threshold concept is like a portal that opens up a new and previously inaccessible way of thinking about something. - These concepts are generally found to be challenging for learners and they can have difficulty in understanding it. --- Meyer, Jan, and Ray Land. "Threshold concepts and troublesome knowledge: Linkages to ways of thinking and practising within the disciplines." (2003). - [Link](https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=b98202852dc631ced19a98414cbd9e9461c10417)