It captures information about IP traffic going into your interfaces.

• VPC Flow Logs
• Subnet Flow Logs
• Elastic Network Interface (ENI) Flow Logs.

Helps to monitor & troubleshoot connectivity issues. Examples: subnet.
    - Subnet to Internet
    - Subnet to Subnet
    - Internet to Subnet

Capture network information from AWS managed interfaces too:
    - ELB
    - ElastiCache
    - RDS
    - Aurora
    - etc.

VPC flow logs data can goto S3, CloudWatch Logs, Kinesis Data Firehouse (which then goes to S3, Redshift, ElastiSearch)