What is the difference between selection and projection ?

When we trying to access data from a database table, selection of rows that match a particular set of values is called selection.

Example:

D:\app\Admin\virtual\virtual\product\12.2.0\dbhome_1\bin>sqlplus/nolog
 SQL*Plus: Release 12.2.0.1.0 Production on Mon Feb 28 10:10:13 2022
 Copyright (c) 1982, 2016, Oracle.  All rights reserved.
 SQL> conn mereba/mereba@orcl
Connected.
 SQL> select * from tbl_customer where customer_type='I';
    CUST_NO CUSTOMER_T CUST_NAME                 COUNTRY         SWIFT_CODE
---------- ---------- ------------------------- --------------- ------------
########## I          Messi John Dave           USA
 SQL>

And  the selection of some of the columns of a table data is also called projection.

Example:

SQL> select cust_name,country from tbl_customer where customer_type='I';
 CUST_NAME                 COUNTRY
------------------------- ---------------
Messi John Dave           USA
 SQL>