SDLC stands for the Software Development Life Cycle is a framework on how tasks should be performed or each step to be followed in the software development process. SLDC is a structure followed by the software development team with an IT organization. This procedure includes detailed planning on how to execute the plan of developing, maintaining & replacing the software. A bug is a kind of virus or fault in the computer system that obstructs specific software to work smoothly. There are various types of software developing life cycles (SDLC). Some of them are as follows: • Waterfall model • V-Shaped model • Spiral Method (SDM) • Agile development • Evolutionary Prototyping Model • Iterative & Incremental Method .Out of all, Waterfall model is the straightforward structure of SDLC method. Developer finishes one method & then he moves forward to the next step. Others are also good & advanced that also give the best results while testing a software or an application. Bugs are generally found during the unit testing conducted by the software developer to test the modules. A defect is identified when the software or an application does not fulfill the required specification. A defect also arises when a tester or the client is operating the system, software or an application.