selector
n. countablen. a person or tool that chooses something from a group. In technology, it is a piece of code that picks which part of a page to change.
n. an agent or mechanism responsible for choosing from a set of options. In computing, specifically CSS, it identifies the HTML elements to which a set of style rules applies.
The CSS selector changes all the headings to blue.
The national team selector watched several matches this weekend to decide which players to invite to the training camp.
By using a more specific selector in the stylesheet, the developer ensured that the custom buttons maintained their unique appearance without affecting the rest of the site's interface.
From select + -or.
In a sporting context, it refers to a person; in a technical context, it refers to a string of characters or a hardware switch.