throbber

A throbber is a graphical user interface element used to indicate that a task is in progress. It functions as a loading indicator, signaling to the user that the system is busy and that no immediate response should be expected. Throbbers are common during network requests, file I/O, or other long-running operations in web pages and applications.

Visual designs vary, with circular spinners being the most recognizable form, but linear progress bars and animated sequences of dots also widely used. Throbbers can operate in an indeterminate state, where the exact progress is unknown, or in a determinate state, where a numeric or proportional progress is shown. Implementations rely on CSS animations, SVG, canvas, or image assets, and are often styled to align with the platform’s visual language.

Accessibility considerations are important: include appropriate ARIA attributes or text labels (for example, aria-label="Loading") and avoid relying on color alone to convey status. If the progress is determinate, communicate percent complete or a progress value for assistive technologies.

Historically, the term throbber has been used in some software development communities, notably in Mozilla projects, to describe the loading spinner. Today, most platforms simply call this a loading indicator or spinner, though the term remains in some documentation and codebases.