Interactive Application Security Testing (IAST) is a technology for automatically identifying and diagnosing software vulnerabilities in applications and APIs. IAST is not a scanner, and instead continuously monitors for vulnerabilities by instrumenting from within your application throughout the software development life cycle (SDLC) and instantly alerts you through the tools you're already using in development and test.
Why do you need IAST? We have a massive "scale" problem in application security with a very limited number of security experts and almost 20 million developers worldwide. Running tools such as SAST, DAST, and SCA requires scarce expertise whereas IAST requires little to no expertise needed.