Oracle E-Business Suite Release 12.2 introduced Online Patching, a feature that greatly reduces the downtime that was needed in previous releases to apply patches and updates. Online Patching minimizes downtime by allowing patching operations to be performed while users remain on the system.
Online Patching features
Here's the official Online Patching documentation:
Here's our official webcast with a primer on Online Patching:
Here's what you need to do to ensure that your customizations work with Online Patching: