List of values accepted by a column Table Animal
has following columns:

SR_ID
First_Name
Last_Name
PET

The PET column has a check constraint; hence it only accepts three values DOG, CAT, FISH.
Sample Data
+-------+-------------+-----------+----------+
| SR_ID |  First_Name | Last_Name |   PET    |
+-------+-------------+-----------+----------+
|     1 |  JOHN       |      D.   |   DOG    | 
|     2 |  MIKE       |      S.   |   CAT    |  
|     3 |  MARIO      |      M.   |   CAT    | 
|     4 |  MICHEAL    |      T.   |   CAT    | 
+-------+-------------+-----------+----------+

How would the admin check (via a query) which values are accepted for the column PET?
Some Background
By running the following query:
Select PET, count(PET) from Animal group by PET

I get the following result:

+-----+------------+
| PET | count(PET) |
+-----+------------+
| CAT |          3 |
| DOG |          1 |
+-----+------------+


The admin only gets DOG and CAT values. It is obvious that FISH won't be found since it is not in the database. How can we know that PET column accepts the value FISH?
DESCRIBE Animal would just list column names and its datatype - not the values accepted.
You can check the condition of the check constraint from all_constraints or user_constraints view. 

SQL&gt; create table animal(
SR_ID number, 
First_Name varchar2(20), 
Last_Name varchar2(20), 
PET varchar2(20) constraint ckpet check (PET in ('DOG', 'CAT', 'FISH'))
);

Table created.

SQL&gt; select constraint_name,search_condition 
from all_constraints
where table_name='ANIMAL'
and constraint_type='C'; 

CONSTRAINT_NAME     SEARCH_CONDITION
---------------     ---------------------------
CKPET                PET in ('DOG', 'CAT', 'FISH')