Walls are ways you can organize your notes, publicy or privately. You can learn more about what you can make these walls into here: What Can I Do with Walls

Historically, walls have been for:

• Inviting families and posting photos
• Organizing company/organization ideas to create better products or services
• Gather people of similar or completely different minds to generate ideas people could make (dreamers and makers, Republicans and Democrats, even just futurists).
• Create boards where new ideas could come to life
• Or simply just to post memes

Walls were originally named like that because the founder/programmer @Andrew would tape notes on his wall whenever a new idea popped in his mind. Whenever he had the time to go back to them, all he needed to do was glance over, snatch a note off the wall, and get to work making an idea a reality.