While you'll need to know many terms to become fluent in cruise speak, here are some basics -- a phrase book, if you will -- to enable you to speak with the natives on your first sailing.
Aft/forward: The back of the ship is aft and the front of the ship is forward. These terms are used as adjectives, such as "aft balcony cabins" or "Deck 8 forward."
Bow/stern: The front part of the ship is called the bow. The back part of the ship is called the stern.
Cabin steward: The person who cleans your cabin and turns down the room at night. A steward can assist with minor tasks such as bringing you ice and taking your laundry to be cleaned.
Closed-loop sailing: An itinerary that begins and ends from the same port – a roundtrip cruise.
Cruise director: The emcee of the cruise who heads up the entertainment staff and might handle passenger requests and complaints.
Cruisetour: A cruise that is preceded or followed by a bus tour, operated by the cruise line.
Friends of Bill W/Friends of Dorothy: Friends of Bill W. is the code name for Alcoholics Anonymous meetings onboard. Friends of Dorothy denotes GLBT activities.
Galley: A ship's kitchen.
Gangway: The ramp or stairway that leads from the ship to the pier, allowing passengers and crewmembers to get on and off the ship.
Guarantee: A fare class that allows the cruise line to select your cabin number, often at a lower price point than an assigned cabin in the same cabin category.
Lido deck: The pool deck.
MDR: Main dining room.
Muster drill/muster station: A muster drill is a mandatory event where passengers assemble in a specific location and receive instructions on what to do in an emergency. The muster station is the location passengers must go to during a drill or in an actual emergency.
OBC: Onboard credit -- a credit added to your onboard account, either as a perk of booking or as compensation for an unforeseen event.
Open-jaw sailing: An itinerary that begins and ends in different ports -- a one-way cruise.
Port/starboard: The nautical terms for left (port) and right (starboard). You can remember because both "left" and "port" have four letters.
Porthole: A round window, often smaller than the standard picture window found in most outside cabins.
Purser: The officer in charge of financial accounting, who handles billing issues, as well as general customer service.
Repositioning or repo cruise: A cruise that begins and ends in different ports as a ship moves from one cruising region to another.
Tender: A small boat that ferries cruise passengers from the ship to shore when docking isn't possible. Also can be used as a verb; i.e. we tendered to shore in Grand Cayman.
And if you need a guide to understanding all the acronyms used on the message boards, here are two threads to allow you to "talk the talk"; one is in the FAQ's and the other in the Holland America forum.