It is a new JVM instruction which allows a compiler to generate code which calls methods with a looser specification than was previously possible — if you know what “duck typing” is, invokedynamic basically allows for duck typing. There’s not too much you as a Java programmer can do with it; if you’re a tool creator, though, you can use it to build more flexible, more efficient JVM-based languages. Here is a really sweet blog post that gives a lot of detail.