NCIS: Season 18 is currently airing on CBS. (Image: CBS) READ MORE What does NCIS stand for? While viewers simply refer to the show as NCIS without giving it a second thought, these letters actually do mean something. The acronym of NCIS stands for Naval Criminal Investigative Services. This means that every investigation that NCIS has looked into has a connection with the marines and the navy. Even though the connection often gets lost within the plot, there is always something that ties it to the navy, meaning it's up to NCIS to look into. NCIS: Agent Deeks and Kensi are trying to have a baby in NCIS Los Angeles. (Image: CBS)