The meteor runtime lets you write asynchronous code in a synchronous style using the Fibers co-routines module. This way, you can make Mongo queries without passing callback after callback while waiting for results. Dynamics is Meteor's implementation of dynamically scoped variables that work with Fibers. Understanding these concepts are a prerequisite to understanding Meteor performance and integration with asynchronous libraries. We'll start off by reviewing what it means to be asynchronous in NodeJS. Then you'll play with fibers using a server side debugger and use them to use an asynchronous function in a synchronous style. Then you'll see how Meteor's bindEnvironment method lets us work with asynchronous code. Finally, you'll learn what a dynamically scoped variable means, and how Meteor implements them in Meteor.EnvironmentVariable.
https://www.eventedmind.com/classes/meteor-fibers-and-dynamics-9ba17f98