PFQuery is one of the key concepts for Parse. It allows you to retrieve PFObjects by specifying some conditions, making it easy to build apps such as a dashboard, a todo list or even some strategy games. However, PFQuery is based on a PULL model, which is not suitable for apps that need real-time support.
Suppose you are building an app that allows multiple users to edit the same file simultaneously like a Chat. PFQuery would not be an ideal tool since you can not know when to query from the server to get the updates.
To solve this problem, we introduce Parse LiveQuery. This tool allows you to subscribe to a PFQuery you are interested in. Once subscribed, the server will notify clients whenever a PFObject that matches the PFQuery is created or updated, in real-time.
Live Query is a PUSH model.