Beginner question: What's the difference between a security group and a Microsoft 365 group?

This is a classic point of confusion when you're starting out. The short answer is their primary purpose: **Security Groups are for securing access to resources, while Microsoft 365 Groups are for collaboration and come with a suite of shared resources.**

Here's the breakdown from an infrastructure/CI-CD perspective:

**Security Group**
* **Purpose:** Pure access control. It's a container for users, devices, or other groups used to assign permissions to resources (e.g., Azure roles, SharePoint sites, file shares).
* **What it gives you:** Nothing but a membership list for authorization checks.
* **Use Case:** "Grant this group 'Reader' access to our Azure Key Vault" or "Allow this group to deploy to the production Kubernetes cluster."

**Microsoft 365 Group**
* **Purpose:** Collaboration first. Creating one automatically provisions a shared set of resources for its members.
* **What it gives you:** A shared mailbox, calendar, SharePoint site, OneNote, Planner, and more (depending on your tenant setup).
* **Use Case:** "We need a team for the 'Project Phoenix' initiative where we can share files, have a team email, and track tasks." It's the backend for a Team in Microsoft Teams.

**Key Practical Difference:**
You use a Security Group to *lock down* something. You create a Microsoft 365 Group to *build out* a collaborative workspace. You can use a Security Group for mailing lists, but you shouldn't use a Microsoft 365 Group for critical resource access unless you understand the membership management implications (e.g., dynamic vs. assigned users).

From an automation standpoint, you target them differently. For instance, granting Azure RBAC via CLI:
```bash
# Assigning a role to a Security Group (common)
az role assignment create --assignee "sg-project-alpha" --role "Contributor" --scope "/subscriptions/xxx/resourceGroups/my-rg"

# You generally wouldn't do this with an M365 Group for resource permissions.
```