The difference between CMM and CMMI is that CMMI integrates the separate models used in CMM, CMMI documents best practices by areas of interest where as CMM looks at functions. CMM uses a 5 level approach, where CMMI uses 22 models to look at a specific objective.
CMM stands for capability maturity model that software companies use to increase consistency, reliability, and predictability based on 5 levels. The 5 levels are based on the best engineering and management practices. CMMI stands for capability maturity model integration, which takes CMM a step further by integrating the function and look at specific interests or business objectives of the software.