A Linked Account is an account created in your Lamden Vault by a website that you have approved to interact with your Lamden Vault. This approval is done via a popup window when you visit the website.
Each website that you interact with will have its own Linked Account. This lets you, as the user, control how much of your TAU that each application has access to.
Decentralized Applications (DAPPS)
DAPPS are applications that have a blockchain comnponent to them. Any application that connects to your Lamden Vault is referred to as a DAPP.