Microsoft Teams is a chat-based collaboration platform that allows users to communicate through chat, audio and video calls, and collaboration using integrated Office 365 apps. It offers enterprise-level security, compliance and manageability. Developers can customize and extend Teams through third party apps, bots, tabs and other integrations. The document provides information on creating custom apps for Teams using various tools and frameworks, and how apps can integrate with services like Azure, Cognitive Services and Microsoft Graph to enable intelligent capabilities within Teams.