# Security Group

A security group is a collection of access control rules for cloud resources, such as cloud servers, containers, and databases, that have the same security protection requirements and that are mutually trusted within a VPC. After a security group is created, you can create various access rules for the security group, these rules will apply to all cloud resources added to this security group.

Your account automatically comes with a default security group. The default security group allows all outbound traffic, denies all inbound traffic, and allows all traffic between cloud resources in the group. Your cloud resources in this security group can communicate with each other already without adding additional rules.

Parent topic: Basic Concepts