Agile Manifesto is a set of best practices which software developers should follow while developing a product. The manifesto was created in 2001. It has four key values and twelve principles. Agile Manifesto offers the software developers a lightweight development process. The core values of Agile Manifesto indulge interactions among the developers and respond to changes. It emphasizes on continuous delivery of the work in contrast to the Waterfall model, regular interactions among the developers and self-organization of teams. Scrum is the framework to implement Agile Manifesto. Scrum framework defines the events, accountabilities, and artifacts to implement the Agile Manifesto. Agile Manifesto was created to overcome the following drawbacks of Waterfall methodologies of software development.

1. Software is produced at the end of the life cycle in Waterfall model. So, this model is not suitable for long term projects.
2. Waterfall model has low probability of success in medium complex projects as there is no scope for continuous adaptation.

Detailed information about the values and principles of Agile Manifesto are given in the following article:

Agile Manifesto Values and Principles (scrumalliance.org)