I'm updating my CV and while browsing my documents I noticed a flattering official statement by two PIs that I worked for. I'd like to list it, but what is such a document called or what would be the best description? To get an idea of what it is, the second paragraphs states: "In general, we have been really impressed by your technical skills and knowledge on genetics and molecular biology. You are motivated, learn new techniques and procedures quickly, and carefully carry out your experiments. You also have a very pleasant personality. It is indeed a great pleasure to have you study in our laboratories". Signed by two associate professors on official paper.