A runtime environment is a collection of software tools and services that allow programs to execute. It provides the necessary resources, such as memory and processing power, and manages the execution of code. This environment ensures that applications run smoothly by handling tasks like memory allocation and input/output operations. Different programming languages have their own specific runtime environments. For example, the Java Runtime Environment (JRE) allows Java applications to run on any device with the JRE installed. Similarly, the .NET Runtime supports applications built with the .NET framework, enabling them to operate across various platforms.