The CLS fields refers to data which takes a format like:
| CLS |
|---|
| AGE, COB, HIQUAL, UNIT |
| AGE, ETHGRNI, GENHEA, LLHPDI, UNIT |
| AGE, HIQUAL, OOTT, UNIT |
The CLS is essentially a combination of topics, sometimes refered to as MNU. What the first row means that the topics AGE, COB, HIQUAL and UNIT exist as a combination for given filters and locations.
For a brief description of what this combination means, you can look at the DKAN_TITLE, which in this case is:
Age by Country of birth by Highest level of qualification 2011
You can also use the codelist_def table to find out what the indvidiiaul topics/MNUs stand for.