Mardi Gras-a carnival held in some countries on Shrove Tuesday (the last day before Lent) but especially in New Orleans.
Bottleneck effect is when there's something that either kills the majority of the population or just prevents it from reproducing. This creates genetic drift because the likelihood of gene prominence changing is much higher in a small population. The Founder Effect is a type of Bottleneck effect. It is when a small amount of individuals starts a population usually due to migration.
After a few generations, the population may look very different from the original population. In rare cases, a bottleneck may even lead to speciation. This article has a great comparison between the Founder's effect and Genetic Drift. Here is an article relating Genetic Drift and Effective population size.