Different phases of SDLC and STLC?

What is quality assurance?
Software QA involves the entire software development PROCESS - monitoring and improving the process, making sure that any agreed-upon standards and procedures are followed, and ensuring that problems are found and dealt with. It is oriented to 'prevention'.

What is the difference between QA and testing?
Testing involves operation of a system or application under controlled conditions and evaluating the results. It is oriented to 'detection'.
Software QA involves the entire software development PROCESS - monitoring and improving the process, making sure that any agreed-upon standards and procedures are followed, and ensuring that problems are found and dealt with. It is oriented to 'prevention'.

Describe the difference between validation and verification
Verification is done by frequent evaluation and meetings to appraise the documents, policy, code, requirements, and specifications. This is done with the checklists, walkthroughs, and inspection meetings.
Validation is done during actual testing and it takes place after all the verifications are being done.

What are SDLC and STLC? Explain its different phases.
SDLC
Requirement phase
Designing phase (HLD, DLD (Program spec))
Coding
Testing
Release
Maintenance

STLC
System Study
Test planning
Writing Test case or scripts
Review the test case
Executing test case
Bug tracking
Report the defect

What is Error guessing and Error seeding?

Error Guessing is a test case design technique where the tester has to guess what faults might occur and to design the tests to represent them.
Error Seeding is the process of adding known faults intentionally in a program for the reason of monitoring the rate of detection & removal and also to estimate the number of faults remaining in the program.