Reliability analysis is in some cases based on some discrete performance parameter like number of successful operation cycles before (the first) failure of a non-repairable product or the number of such cycles between successive failures of a repairable equipment or the number of units in a group put on test which fail before a specified time. Further, even when the reliability parameter is time to failure or time between successive failures, and hence measurable on a continuous scale, observations as recorded may invite discrete probability models for analysis. Quite often, we get lifetime data grouped into class intervals, requiring some discrete models as appropriate. Hence, the application of discrete probability models has been growing over the years.