Define the term “bootloader” in the context of operating systems.

A bootloader is a critical piece of software in the startup process of a computer system. Its primary function is to load the operating system into memory when the system is powered on or restarted. This process is essential because, without a bootloader, the operating system would not be able to initialize and run properly.

The bootloader executes immediately after the firmware (like BIOS or UEFI) completes its self-tests and initializes hardware components. It locates the operating system on the storage device, loads it into the system’s RAM, and then transfers control to it, effectively transitioning the system from a powered-off state to a fully operational state with the operating system running.

The other choices refer to functionalities that are not associated with a bootloader. Security for applications is managed through various security features and measures within the operating system, user interface elements are handled by the operating system’s graphical environment or window manager, and data encryption is a separate function often managed within the operating system's features or applications. Thus, the definition of a bootloader as the component that loads the operating system is essential for understanding its role in the boot process of computing devices.