Internet applications have been used exponentially all the world. Distributed Denial of Service attack (DDoS) is prominent attack that disrupts the normal execution of web server and its resources. The situation even become worse with the irruption of Flash events (FE). So, it is very imperative to distinguish between Flash Events and DDoS attacks based on some packet or flow parameters. Both DDoS and FE cause congestion on the network server as a result delays in web services, that causes significant financial losses, therefore it requires proactive and quick measures. This paper provides comprehensive review about flash events as well as DDoS attacks and it repeats some of strategies that are already published. In this paper, we are providing details about different parameters to categorize flash events from DDoS. This paper helps the community to understand the problem in better way through characterization of DDoS attacks and FE.