Based on Oracle Metalink 398942.1. Upon installation of Oracle Applications, a number of schema (sometimes called ORACLE schema) are present in the database. You do not need to create these schema; however, you should change the default passwords.
These schema come from different sources and can be described as being of the following types:

1. Schema that exist in every Oracle database (whether used by Oracle Applications or not) [ex: SYS,SYSTEM].

2. A small set of schema used by shared components of Oracle Applications [for example, APPLSYSPUB,APPLSYS,APPS].

3. A large set of schema provided by the individual products of Oracle Applications [for example, ABM,AHL,...,ZSA,ZX].

4. A set of schema that belong to optional database features or third party products these fall into three subtypes:

1. Used by and patched with Oracle Applications [for example, CTXSYS, PORTAL30].
2. Used by Oracle Applications but patched only with the RDBMS [for example, MDSYS,ORDSYS]
3. Not used by Oracle Applications [for example, SCOTT]

At no time do any of the schema provided with Oracle Applications relate to a particular Oracle Applications user.

All types of schema are used during run time operations of Oracle Applications and the schema of type 2, 3 & 4.1 are accessed during initial installation and patching.

For schema passwords, Oracle Applications concerns itself with mainly three passwords for its schema:
1. A password for APPLSYSPUB (also known as the GATEWAY user). The default password is ‘PUB’.
2. A password shared between APPLSYS and APPS (also known as FNDNAM). The default password is ‘APPS’.
3. A password for all of the product-specific base schema (type 3). The default password for these schema is same as the schema name.

Important: You should change these passwords upon installation.

To change all ORACLE (type 3) schema passwords:

Use this command to change the passwords of all schemas provided by Oracle Application products.

FNDCPASS 0 Y ALLORACLE 

Use the above command with the following arguments. When specifying the ALLORACLE token, FNDCPASS expects the next argument to be the new password.

logon : The Oracle username/password.

system/password : The username and password for the SYSTEM DBA account.

new_password : The new password.

For example, the following command changes all ORACLE schema passwords to “WELCOME”:

FNDCPASS apps/apps 0 Y system/manager ALLORACLE WELCOME

Patch 4926128 contains a SQL script that will list all open accounts with default password in your database.