what is regression in software testing code example

Example 1: what is regression testing

Regression testing is testing existing 
software applications to make sure that
a change or addition hasn’t broken any 
existing functionality. Its purpose is 
to catch bugs that may have been accidentally
introduced into a new build or release candidate, 
and to ensure that previously eradicated 
bugs continue to stay dead.

Example 2: regression suite

It depends on the project.
In my current project out of 800 test cases 
in regression suite around %90 is automation.
We use 10 vm to perform parallelexecution it takes
2 hours to execute depends on the test data.