doc: update glossary
The absence of a value, i.e. `keyValue (key) == NULL`.
- **pop**:
- used in `ksPop()` and @ref KDB_O_POP means to remove
- a key from a keyset.
+ Used in `ksPop()` and `KDB_O_POP` means to remove a key from a keyset.
- **delete**:
- or abbr. del, used in `keyDel()`, `ksDel()` and @ref KDB_O_DEL means to free a key or keyset. The memory
+ or abbr. del, used in `keyDel()`, `ksDel()` and `KDB_O_DEL` means to free a key or keyset. The memory
can be used for something else afterwards.
- **remove**:
- means that the key-value information in the physical database will be removed permanently.
+ Means that the key-value information in the physical database will be removed permanently.
+ Also used to describe removing a particular key from a keyset.
