Agile is a project management discipline for IT/Software industry. Agile software development process is based on an incremental and iterative approach.
Scrum is a subset of Agile. It is a lightweight process framework for agile development.
A Scrum team is cross-functional, maintaining a flat team structure instead of hierarchical one. There are no project managesrs or team leaders in the traditiaonal sense. Ideal team members are 5-9 people.