Web 2.0 refers to the second generation of the World Wide Web, which is characterized by the transition from static webpages to dynamic or user-generated content and the growth of social networking. It's often described as the "read-write" web, where users are not just consumers of content but also creators. Here are some key aspects of Web 2.0:

1. **Interactivity**: Web 2.0 websites allow users to interact with each other and the website itself, creating a user-centric experience through comments, reviews, and social media.

2. **User-Generated Content**: Platforms like blogs, wikis, and social media sites rely heavily on user-generated content, which allows users to contribute information and content.

3. **Social Networking**: The rise of social media platforms like Facebook, Twitter, and LinkedIn has defined this era, enabling people to connect, share, and communicate online more easily.

4. **Rich Internet Applications (RIAs)**: Technologies such as AJAX, Flash, and later HTML5 allowed for the creation of web applications with desktop-like functionality.

5. **Collaboration and Sharing**: Services like Google Docs and Wikipedia exemplify the collaborative nature of Web 2.0, allowing multiple users to contribute and edit content.

6. **Cloud Computing**: The use of cloud services became more prevalent, with companies like Amazon Web Services providing the backbone for many Web 2.0 services.

7. **E-commerce and Online Marketplaces**: Platforms like eBay, Amazon, and Alibaba transformed how we buy and sell goods, relying on user participation and reviews.

8. **Search Engine Optimization (SEO)**: As search engines like Google became the primary means of navigating the web, optimizing content to rank higher in search results became a significant focus for web developers and content creators.

9. **Personalization**: Websites began to offer personalized experiences, using data to tailor content to individual users, such as recommended products on Amazon or personalized news feeds on Facebook.

10. **Mobile Web**: With the advent of smartphones, the internet became more accessible on the go, leading to a surge in mobile applications and responsive web design.

Web 2.0 is not defined by a specific technical update, but rather by changes in the way web pages are designed and used—a focus on user-friendly, interactive experiences. It has been the dominant form of the web since the early 2000s and continues to evolve with new technologies and platforms.