Selectors are patterns used in CSS (Cascading Style Sheets) to target specific elements on a webpage. They allow developers to apply styles, such as colors, fonts, and layouts, to particular elements like divs, paragraphs, or headings. By using selectors, you can control the appearance of your website without altering the HTML structure. There are various types of selectors, including class selectors, which target elements with a specific class attribute, and ID selectors, which target unique elements with a specific ID. Additionally, element selectors can be used to style all instances of a particular HTML tag, such as all h1 headings on a page.