MIM Guide

Glossary

Key Terms & Definitions

Essential terminology for IT Major Incident Management, drawn from ITIL, Agile/SRE, and industry best practices.

Blameless Culture

Agile

An organizational principle where the focus is on understanding system failures rather than assigning individual blame. Essential for honest post-incident reviews and continuous learning.

Blast Radius

Core

The scope of impact of an incident or a change, meaning how many users, services, or systems are affected.

Bridge Call

Process

A conference call or virtual meeting room where the incident response team collaborates in real-time during a major incident. Also called a War Room.

Change Management

ITIL

The ITIL process that controls changes to the IT environment. Critical during incidents because most incidents are caused by changes.

Chaos Engineering

Agile

The discipline of deliberately introducing controlled failures into a system to test its resilience and identify weaknesses before they cause real incidents.

CMDB (Configuration Management Database)

ITIL

A database that stores information about IT assets and their relationships. Used during incidents to understand service dependencies and blast radius.

Escalation

Core

The process of involving additional or more senior resources. Functional escalation involves technical experts; hierarchical escalation involves management.

Feature Flag

Agile

A software technique that allows features to be toggled on/off without deploying new code. Useful during incidents for quick rollback of problematic features.

Game Day

Agile

A planned exercise where a team simulates a major incident to practice the response process, test runbooks, and identify gaps in a safe environment.

KEDB (Known Error Database)

ITIL

A database of known errors and their workarounds. Checked during incidents to see if the issue has a known solution.

Major Incident

Core

An incident with significant business impact that requires an emergency response beyond the normal incident management process. Typically involves multiple teams and executive visibility.

MIM (Major Incident Manager)

Roles

The designated person who takes ownership of the major incident response, coordinating teams, driving communications, and ensuring the process is followed. Also known as Incident Commander.

MTBF (Mean Time Between Failures)

Metrics

The average time between incidents for a given service. Measures reliability over time.

MTTA (Mean Time to Acknowledge)

Metrics

The average time between when an alert is triggered and when a responder acknowledges and begins working on it.

MTTD (Mean Time to Detect)

Metrics

The average time between when an incident begins and when it is detected by monitoring or reported by users.

MTTR (Mean Time to Resolve)

Metrics

The average time from incident detection to full service restoration. The primary metric for measuring incident management effectiveness.

PIR (Post-Incident Review)

Process

A structured, blameless meeting held after a major incident to analyze what happened, identify root causes, and define improvement actions. Also called a Retrospective or Post-Mortem.

Problem Management

ITIL

The ITIL process responsible for identifying root causes and driving permanent fixes to prevent incident recurrence. Takes over from incident management after service is restored.

RACI Matrix

Process

A responsibility assignment tool: Responsible (does the work), Accountable (owns the outcome), Consulted (provides input), Informed (kept up to date).

RCA (Root Cause Analysis)

Process

A systematic process for identifying the underlying cause(s) of an incident. Common techniques include 5 Whys, Fishbone Diagram, and Fault Tree Analysis.

Runbook

Process

A documented set of step-by-step procedures for handling specific operational scenarios. Used during incidents to ensure consistent response.

Severity (SEV)

Core

A classification level indicating the impact and urgency of an incident. Typically ranges from SEV-1 (most critical) to SEV-4 (lowest). Used to determine response speed and communication cadence.

SLA (Service Level Agreement)

ITIL

A formal agreement between a service provider and customer defining expected service levels (availability, response time, etc.) and penalties for non-compliance.

SLO (Service Level Objective)

ITIL

An internal target for service reliability. More flexible than SLAs. Used by SRE teams to balance reliability investment with feature development.

Swarming

Agile

An Agile-inspired approach where multiple experts are brought together immediately to work on an incident collaboratively, rather than following a tiered escalation path.

Workaround

Core

A temporary solution that restores service or reduces impact while a permanent fix is developed. Not the same as a resolution.