IBM Db2 is a relational database system from IBM for mission-critical workloads. According to IBM, it stores transactional, analytical and vector data on one platform and automates parts of tuning and administration. Db2 is available as self-managed software on your own premises, as IaaS on IBM Cloud or AWS, as containers on Red Hat OpenShift or Kubernetes, and as a fully managed SaaS on IBM Cloud or AWS. Amazon RDS for Db2 is also offered on AWS. The software comes in several editions, from a free Community edition to Standard and Advanced.
IBM is a US company, and Db2 is commercial, proprietary software. Where the data resides depends on the chosen option: with self-managed installations you decide, while with the SaaS offerings the database runs on the infrastructure of IBM or AWS, both US providers. The SaaS on IBM Cloud offers a disaster-recovery node in another region. For European organisations, the choice of region and the provider's legal jurisdiction are therefore separate points to assess.