What type of change is often used for resolving incidents or implementing security patches?

A change that must be implemented as soon as possible without strictly following the standard process e.g. to resolve an incident or implement a security patch.

The process for assessment and authorization is expedited to ensure quick implementation, so scheduling and documentation is not a priority.

The change authority may be separate from what is standard or normal practice, typically smaller in number but with greater capacity to expedite approval.

https://www.bmc.com/blogs/itil-change-enablement/