ArcGIS Online is a cloud-based mapping and analysis platform. While functionality is limited compared to desktop versions, ArcGIS Online includes everything you need to create web maps, create 3D web scenes, create web apps, and create notebooks. Through Map Viewer and 3D Scene Viewer, you can access a gallery of basemaps and smart styles for exploring and visualizing your data. You also have access to templates and widgets for creating web apps that you can publish to ArcGIS Online. Additionally, using ArcGIS Notebooks, you can access Python resources to perform analysis, automate workflows and visualize data.
ESRI's ArcGIS Online Help Page
