Certificate of Sixth Year Studies
In the Scottish secondary education system, the Certificate of Sixth Year Studies (CSYS) was the highest level of qualification available to pupils from 1968 until circa 2000. Overseen by the Scottish Examination Board (SEB), it was taken by students in their sixth year (final year) of secondary education (ages 16–18) and was available for a range of different subjects.
Source: Wikipedia — Certificate of Sixth Year Studies (CC BY-SA 4.0)