WordPress blocks are a new way to create and organize content in WordPress editor (i.e. Gutenberg Block Editor or Block Editor) introduced in the version 5.0 of the WordPress. Now every element like paragraph, heading, quote, code etc. is a WordPress block with customization options which allows the user to have more control over the design and presentation of the content.

Blocks treat Paragraphs, Headings, Media, and Embeds all as components that, when strung together, make up the content stored in the WordPress database, replacing the traditional concept of freeform text with embedded media and shortcodes. The new editor is designed with progressive enhancement, meaning that it is back-compatible with all legacy content, and it also offers a process to try to convert and split a Classic block into equivalent blocks using client-side parsing. Finally, the blocks offer enhanced editing and format controls.

https://developer.wordpress.org/block-editor/

Features of WordPress Blocks:

• Allow user to focus on creating the content without worrying about the underlying technicalities
• The appearance of the content added via blocks can be customized using the block settings/ options
• The blocks can be dragged and dropped to adjust the position in page layouts
• The blocks can be duplicated, made reusable and grouped
• The blocks can be transformed to other supported block types
• Custom blocks can be added using the Block API
• The behavior/appearance of existing blocks can be modified as well

List of Default WordPress Blocks (66):

Common – WordPress Blocks:

1. Paragraph
2. Heading
3. List
4. Quote
5. Image
6. Gallery
7. Audio
8. Cover
9. File
10. Video

Formatting – WordPress Blocks:

1. Code
2. Table
3. Classic
4. Custom HTML Code
5. Preformatted
6. Pull-quote
7. Verse

Layout Elements – WordPress Blocks:

1. Button
2. Columns
3. Group
4. Media & Text
5. More
6. Page Break
7. Separator
8. Spacer

Widgets – WordPress Blocks:

1. Shortcode
2. Archives
3. Calendar
4. Categories
5. Latest Comments
6. Latest Posts
7. RSS
8. Search
9. Tag Cloud

Embeds – WordPress Blocks

1. Embed
2. WordPress
3. Twitter
4. YouTube
5. Facebook
6. Instagram
7. SoundCloud
8. Spotify
9. Flicker
10. Vimeo
11. Animoto
12. Cloudup
13. Crowdsignal
14. Dailymotion
15. Hulu
16. Imgur
17. Issuu
18. Kickstarter
19. Meetup.com
20. Mixcloud
21. Reddit
22. Reverbnation
23. Screencast
24. Scribd
25. Slideshare
26. Smugmug
27. Speaker deck
28. TED
29. Tumbler
30. VideoPress
31. WordPress.tv
32. Amazon Kindle

References:

• https://developer.wordpress.org/block-editor/