diff --git a/knowledge base/cloud computing/aws/README.md b/knowledge base/cloud computing/aws/README.md
index 0ccb9fd..acaf650 100644
--- a/knowledge base/cloud computing/aws/README.md
+++ b/knowledge base/cloud computing/aws/README.md
@@ -1,5 +1,6 @@
# Amazon Web Services
+1. [TL;DR](#tldr)
1. [Networking](#networking)
1. [Elastic IP addresses](#elastic-ip-addresses)
1. [Services](#services)
@@ -20,6 +21,36 @@
1. [Further readings](#further-readings)
1. [Sources](#sources)
+## TL;DR
+
+_Regions_ are physical world locations where multiple Availability Zones exist.
+They are physically isolated and independent from one another.
+Regions come at **no** charge.
+
+_Availability Zones_ are sets of one or more data centers, each with their own resources, housed in separate facilities.
+
+Resources created in one Region do **not** exist in any other Region, unless explicitly using replication features
+offered by AWS services.
+Some services like IAM do **not** have Regional resources.
+
+Recommended using regional STS endpoints instead of [the global one](https://sts.amazonaws.com) to reduce latency.
+Session tokens from regional STS endpoints are valid in **all** AWS Regions. However, tokens from the global endpoint
+are only valid in enabled Regions.
+
+Session tokens valid in all Regions are larger. If storing session tokens, these might affect one's systems.
+
+Regions introduced before 2019-03-20 are enabled by default. Newer regions are now disabled by default.
+Regions enabled by default **cannot be enabled or disabled**.
+
+Disabling Regions disables IAM access to resources in those Region. It will **not** delete resources in the disabled
+region, and they **will** continue to be charged at the standard rate.
+
+Disabling a Region can takes a few minutes to several hours to take effect. Services and Console will be visible until
+the region is completely disabled.
+
+Enabling Regions takes a few minutes to several hours. They **cannot** be used until the preparation process is
+complete.
+
## Networking
VPCs define isolated virtual networking environments.
@@ -338,6 +369,7 @@ creation of non-compliant resources.
- [Guidance for Tagging on AWS]
- [Creating organization policies with AWS Organizations]
- [AWS re:Invent 2022 - Advanced VPC design and new Amazon VPC capabilities (NET302)]
+- [Enable or disable AWS Regions in your account]