What do the letter codes in Oracle user_contraints table's constraint_type column stand for?

Question

select distinct constraint_type from user_constraints;

C
-
C
P
R
U

Seems P means primary key and R means foreign key, correct? What are U and C?

Answer 1

Type Code   Type Description   Acts On Level
C   Check on a table  Column
O   Read Only on a view  Object
P   Primary Key  Object
R   Referential AKA Foreign Key  Column
U   Unique Key  Column
V   Check Option on a view  Object

Answer 2

CONSTRAINT_TYPE (from 11gR2 docs)
C - Check constraint on a table
P - Primary key
U - Unique key
R - Referential integrity
V - With check option, on a view
O - With read only, on a view
H - Hash expression
F - Constraint that involves a REF column
S - Supplemental logging