four i would say, built in functions, plus three kinds of user defined functions: scalar, multi statement table functions and inline table functions.

-edit]

from my notes of SQL server object types, i didn't include agragate functions or CLR types in the offhand list above:

OBJECT TYPES

AF = Aggregate function (CLR)AGGREGATE_FUNCTION

C = CHECK constraintCHECK_CONSTRAINT

D = DEFAULT (constraint or stand-alone)DEFAULT_CONSTRAINT

F = FOREIGN KEY constraintFOREIGN_KEY_CONSTRAINT

FN = SQL scalar functionSQL_SCALAR_FUNCTION

FS = Assembly (CLR) scalar-functionCLR_SCALAR_FUNCTION

FT = Assembly (CLR) table-valued functionCLR_TABLE_VALUED_FUNCTION

IF = SQL inline table-valued functionSQL_INLINE_TABLE_VALUED_FUNCTION

IT = Internal tableINTERNAL_TABLE

P = SQL Stored ProcedureSQL_STORED_PROCEDURE

PC = Assembly (CLR) stored-procedureCLR_STORED_PROCEDURE

PG = Plan guidePLAN_GUIDE

PK = PRIMARY KEY constraintPRIMARY_KEY_CONSTRAINT

R = Rule (old-style, stand-alone)RULE

RF = Replication-filter-procedureREPLICATION_FILTER_PROCEDURE

S = System base tableSYSTEM_TABLE

SN = SynonymSYNONYM

SQ = Service queueSERVICE_QUEUE

TA = Assembly (CLR) DML triggerCLR_TRIGGER

TF = SQL table-valued-functionSQL_TABLE_VALUED_FUNCTION

TR = SQL DML triggerSQL_TRIGGER

TT = Table typeTABLE_TYPE

U = Table (user-defined)USER_TABLE

UQ = UNIQUE constraintUNIQUE_CONSTRAINT

V = ViewVIEW

X = Extended stored procedureEXTENDED_STORED_PROCEDURE