[Aaargh20318]

To my understanding it’s an actual subset of Java, a very limited subset, but a subset of the real Java nonetheless. Java Card applets are compiled using a real Java compiler, and then the bytecode is translated into a simplified format for running on the card.

[Silasdev]

This video from defcon gives a good overview of what Java Card applets is, the limitations and what it can do: https://www.youtube.com/watch?v=31D94QOo2gY