Quality is delighting customers
Test Closure activities fall into four major groups.
Test Completion Check: To ensure all tests should be either run or deliberately skipped and all known defects should be either fixed, deferred for a future release or accepted as a permanent restriction.
Most of the software testing services perform below mentioned tasks of Test Closure activities in Software Testing:
Below answer has explained it very nicely.
In addition to that, creating Test Summary Report (TSR) or Test Closure Report is the main practice and major artifact
Below is an awesome article 6 Easy Steps to Write Test Summary Report (TSR) or Test Closure Report – Free Sample TSR to download
Hope this helps !