CSS3 is the latest version of the Cascading Style Sheets (CSS) language used for describing the presentation of a document written in markup language like HTML. It is the successor to CSS2 and brings many new features and improvements to enhance the look and feel of web pages.

Some of the key features and enhancements introduced in CSS3 include:

1. Selectors: CSS3 introduces new selectors to target elements more efficiently, such as attribute selectors, :not() selector, :nth-child(), and more.

2. Box Model: Additional properties and values are added to manipulate the box model, including border-radius, box-shadow, and box-sizing.

3. Typography: New text properties are introduced to control text styles, such as text-shadow, text-overflow, and text-justify.

4. Background and Borders: CSS3 provides more control over backgrounds and borders with properties like background-size, background-clip, border-image, and border-radius.

5. Transitions and Animations: CSS3 allows the creation of smooth transitions and animations without requiring JavaScript or Flash. Properties like transition, animation, and keyframes are used to define and control animations.

6. Media Queries: Media queries in CSS3 enable responsive web design by applying different styles based on the characteristics of the device or viewport, such as screen width or device orientation.

7. Flexbox and Grid Layout: CSS3 introduces flexible box layout (flexbox) and grid layout systems, which provide powerful methods for creating flexible and responsive page layouts.

8. 2D and 3D Transformations: CSS3 enables the transformation of elements in 2D (such as scaling, rotation, skewing) and 3D (perspective, rotation, translation) using properties like transform and perspective.

Overall, CSS3 provides web developers with a wide range of new tools and techniques to create more sophisticated and visually appealing web pages.