Pertaining to an employment reference letter requested while the employee is still working in this position, without having given notice. Especially important in Germany ("Zwischenzeugnis").
Taken from this question:
In the German-speaking areas (mainly Germany, also Switzerland and Austria), you are legally entitled to an Arbeitszeugnis if you leave a job. An Arbeitszeugnis, literally "work report card" or "job report card", is a two-page letter that gives the dates of your employment, your duties and an indication of how well you performed. You will enclose previous Arbeitszeugnisse with subsequent applications. An Arbeitszeugnis essentially plays the role of references in the US.
If you are still employed at your current job and have been so for multiple years, your last Arbeitszeugnis - from your previous employer - is multiple years old and does not reflect your more recent experience. In such a case, you can request a Zwischenzeugnis (literally "interim report card") from your current employer, which you would then use in applications along with previous Arbeitszeugnisse.
Arbeitszeugnisse and Zwischenzeugnisse are a fundamental part of the workplace in germany (compare relieving-letter in india), with many, many lawsuits especially about how honest an employer can be in assessing your performance. By now, a certain "codespeak" has developed. For instance, your Arbeitszeugnis might say that you "always strove enthusiastically to fulfill your duties" - which you should translate into "strove enthusiastically, but did not manage to". Fun stuff.