"Feedback" is information that you get from people about something that you did. In the example above, the people who read the speaker's blog told him what they thought of his photos. Some other examples of "feedback" include:

• results from a survey of your customers
• classmates giving you advice on how to improve your writing
• the noises that an audience makes when you're performing a play

People use feedback to help them improve a product, performance, etc. which they made.