Android app development is the process of creating software applications for devices running the Android operating system. Android, developed by Google, is the most widely used mobile operating system in the world, powering smartphones, tablets, wearables, and even TVs.

iOS app development refers to the process of building applications for devices that run on Apple's iOS operating system, including iPhones, iPads, Apple Watches, and Apple TVs. iOS app development involves using Apple's official tools, programming languages, and frameworks to create apps that deliver a seamless, intuitive, and high-performance experience to users.

React Native is an open-source framework developed by Facebook that allows developers to build mobile applications using JavaScript and React. It enables the development of cross-platform applications for iOS and Android using a single codebase, providing a seamless experience across both platforms.

Hybrid app development refers to the process of building mobile applications that are designed to run on multiple platforms (iOS, Android, etc.) using a single codebase. Unlike native apps, which are developed separately for each platform, hybrid apps use web technologies such as HTML5, CSS3, and JavaScript wrapped inside a native container, allowing them to run seamlessly on different devices.

Cross-platform app development refers to the practice of building mobile applications that can run on multiple platforms, such as iOS, Android, and others, using a single codebase. The primary goal is to create an app that provides a native-like experience on all platforms without the need for separate development efforts for each one.