diff --git a/en-US/M.xml b/en-US/M.xml
index d16639b..94d7db4 100644
--- a/en-US/M.xml
+++ b/en-US/M.xml
@@ -219,6 +219,27 @@
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+ mission-critical
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+ adj. Write as shown.
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+ Use to refer to software or systems that are essential to fulfilling the core purpose of an organization.
+ When mission-critical systems fail, the impact is often immediate and always severe.
+ Mission-critical software can include customer-facing software for ensuring safety and regulatory compliance and core back-end systems, such as databases and enterprise resource planning (ERP) systems.
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+ To continue to accomplish its core mission, Red Hat considers software to be mission-critical if it is essential to preventing major loss or sustaining health and safety, data or software security, or regulatory compliance.
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+ Examples of failures that are not considered as mission-critical include an outage for routine maintenance, or a system that is down but is not directly affecting customers.
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+
Montecito