STLC-Software Test Life Cycle and SDLC is whole Software 
Development Life Cycle

STLC: It is the s/w test life Cycle
SDLC: It is the total S/w Development life cycle

STLC is software test life cycle it starts with 
1. preparing the test strategy
2. preparing the test plan
3. creating the test environment
4. writing the test cases
5. creating test scripts
6. executing the test scripts
7. analysing the results and reporting the bugs
8. doing regression testing
9. test exiting


SDLC is software or system development life cycle

phases are...
1. project initiation
2. requirement gathering and documenting
3. designing
4. coding and unit testing
5. integration testing
6. system testing
7. installation and acceptance testing
8. support or maintenance

SCM and SQA will follow throughout the cycle

1. Test Plan-> Scope of testing,Testing Strategy,Testing
Techniques,Mile stone,Entry & Exit Criteria,Test case Format
,Bug Reporting Format Etc.

2. Test Analysis-> Split the work in small parts..e.g Test
Scenario then Test cases then Test Scripts.
Decide Different-2 matrices to analysis the work
Decide which Part of Application will test manually and
which will be automated.
how much time retesting or regression will be done.

3. Executing the test case

4. Analysis the Result & bug Reporting

5. Regression Testing

the major diff. b/w sdlc and stlc ,
in sdlc we can coding but in stlc we can not implement the 
coding phase.

STLC means Software Testing Life Cycle
SDLC means Software Development Life Cycle.

STLC is the part of SDLC

Software testing life cycle having some phase 
1 Test requirement 
2 Test plan 
3 Test environment 
4 Test design
5 Test execution and defect track
6 Test report summery and acceptance .
 SDLC having some phase
1 Information gathering
2 SRS prepairing
3 Design
4 coding
5 testing
6 support and maintenace

testing is the part of SDLC

STLC:-
1.Test Strategy/Requirment
2.Test Plan
3.Test Enviornment
4.Test Cases
5.Test Scripts
6.Reporting 
7.Regression Test

SDLC:-
1.Recognization of need
2.Feasble study
3.System Design
4.Coding
5.Testing
6.Implementation
7.Maintinence