Office 365 (now primarily branded as Microsoft 365) is Microsoft's cloud-based productivity suite that combines familiar desktop applications like Word, Excel, and PowerPoint with cloud services such as OneDrive, SharePoint, and Teams. Originally launched as a subscription alternative to perpetual Office licenses, it has evolved into a comprehensive collaboration platform that enables real-time co-authoring, cloud storage, and seamless cross-device access. The key distinction to understand: while Office 365 focused primarily on productivity applications, Microsoft 365 bundles those same apps with advanced security, device management, and compliance tools—making it essential to verify which features your specific subscription plan includes, as capabilities vary significantly across Personal, Business Basic, Business Standard, Business Premium, and Enterprise (E3/E5) tiers.