Northern Blot is a laboratory technique used to detect specific RNA molecules within a sample. It involves the separation of RNA by size through gel electrophoresis, followed by transfer to a membrane. Once on the membrane, the RNA is fixed in place and can be probed with labeled complementary DNA or RNA sequences to identify the target RNA. This method is particularly useful for studying gene expression, as it allows researchers to measure the abundance of specific mRNA transcripts. By comparing the levels of RNA in different samples, scientists can gain insights into cellular processes and the effects of various treatments or conditions.