Testing Pyramid: https://automationpanda.com/2017/10/14/bdd-101-unit-integration-and-end-to-end-tests/
Regression test check that previously developed and tested software still performs after a change.
https://en.wikipedia.org/wiki/Regression_testing
Validation is the process of checking whether the specification captures the customer needs; build the right thing.
Verification is the process of checking that the software meets the specification; build it right.