A quick Google search will tell you that a crypto mixer service (aka a tumbler) is a service designed to obscure the origin and destination of cryptocurrency transactions by blending potentially identifiable funds with others. While intended to enhance privacy, these services are heavily associated with money laundering and other illegal activities, leading to significant regulatory scrutiny and legal action. This should make your BSA/AML/CFT alarm bells go off and is something institutions need to have an understanding of and be on the lookout for as cryptocurrency becomes more and more prevalent.
Kevin explains more in the video.