Unit testing is done in bit and pieces. Like e.g. in SD standard order cycle; we do have 1-create order, then 2-delivery, then 3-transfer order, then 4-PGI and then 5-Invoice. So we will be testing 1,2,3,4 and 5 separately alone one by one using test cases and test data. We will not be looking and checking/testing any integration between order and delivery; delivery and TO; TO and PGI and then invoice.
Whrereas System testing you will be testing the full cycle with it's integration, and you will be testing using test cases which give a full cyclic test from order to invoice.
Security testing you will be testing different roles and functionalities and will check and signoff.
Performance testing is referred to as how much time / second will take to perform some actions, like e.g. PGI. If BPP definition says 5 seconds for PGI then it should be 5 and not 6 second. Usually it is done using software.
Regression testing is referred to a test which verifies that some new configuration doesnot adversely impact existing functionality. This will be done on each phase of testing.
User Acceptance Testing: Refers to Customer testing. The UAT will be performed through the execution of predefined business scenarios, which combine various business processes. The user test model is comprised of a sub-set of system integration test cases.