Also know as System Design Life Cycle and Software Development Life Cycle, WikiPedia's definition of SDLC is "the process of developing information systems through investigation, analysis, design, implementation and maintenance".
To reiterate the major concept, there are the following phases (some of which overlap during the cycle):
Feasibility Study
A documented concensus that the project or upgrade requested will be successful for the effort involved. An objective or group of objectives should be understood prior as the root of the analysis. Aspects such as cost (time, money, effort), other alternatives, and constraints on existing and future solutions, should be investigated and documented.
Analysis and Specifications
This is to analyse the existing and proposed needs of the end users, detailing them to be used as cornerstones of design and testing.
Design, Documentation and Quality Assurance
Based on the agreed upon specifications, design objectives will be clearly defined. As the design is finalised, this will be used as the basis for User and Technical documentation. Quality Assurance such as automated testing can be catered for in the design. Overall a more focused effort is possible during the design of the system. Prototyping and use of programming stubs
Development
Apart from coding, items such as Change Control and policies for Third Party Library dependencies should be considered.