This is an effort to compile a list of all of the various abbreviations and acronyms that you will see on this site. I am sure there are many more that I did not think of. Feel free to add more. Some of these terms are specific to fishkeeping and some are in general use in chats and BBS sites.

• ' - Feet. A distance measure used in the US customary system of units.
• ” - Inches. A distance measure used in the US customary system of units.
• AC - Aquaclear brand of power filters
• AFAIK - As Far AS I KNow
• B&M - Brick and Mortar (an actual shop as opposed to an online store)
• CL - Caudal Length of a fish. See SL.
• cm - centimeter. A unit of length commonly used in the old metric system, but not in the International System of Units.
• EBO - EBO Jager brand of aquarium heaters
• Emp - Emperor brand of power filters
• FWIW - For What Its Worth
• Gal - Since the membership is predominately American, this normally refers to US gallons
• unless otherwise specified.
• GH - General Hardness. A measure of the total concentration of Mg++ and Ca++ expressed in Ca++ equivilants.
• GPH - Gallons (US) Per Hour
• HITH - Hole In The Head disease. A form of Lateral Line Erosion.
• HTH - Hope This Helps
• HOB - Hang On the Back filter (same thing as a power filter)
• IMO - In My Opinion
• IMHO - In My Humble Opinion
• IMNSHO - In My Not So Humble Opinion
• IBTL - In Before The Lock (Done when someone thinks that a post is controversial and will be locked by a moderator. Basically, the person wants to have some involvement with a controversial thread, but does not want to do anything to get them in trouble.)
• KH - carbonate hardness (from the German Karbonathaerte). More properly called alkalinity. Measures alkalinity in equivilant mg CaCO3/l
• l - liter. A popular volume unit from the old metric system. It is not used in the International System of Units.
• LLE - Lateral Line Erosion disease.
• LFS - Local Fish Store
• LMAO - Laughing My [rear end] off.
• lph - Liters Per Hour
• lpf - Liters Per Flush. This has nothing to do with fishkeeping, or the internet for that matter, but I am sure it has perplexed more than one drunken male.
• LPS - Local Pet Store
• LMK - Let Me Know
• - Laughing Out Loud
• LOLPIMP - Laughing Out Loud, [urinating] In MY Pants
• mm - millimeter. A unit of length in the International System of Units
• OTOH - On The Other Hand
• pH - From the latin ponus hydroneus, or power of hydrogen. It is a measure of whether a liquid is an acid, neutral or a base.
• ppm - Parts per million. Usually reported on a weight basis. In most aquaria-related situations, ppm is equivilant to mg/l.
• ROFL - Rolling On the Floor Laughing.
• RTM - Read The Manual
• RTFM - Read The [freakin] Manual
• SL - Standard Length of a fish measured from the tip of the mouth to the beginning of the caudal (tail) fin. This is the preferred method for reporting the length of a fish. It is also called “CL” or Caudal Length.
• TL - Total Length of a fish measured from the tip of the mouth to the tip of the tail. This is the method of reporting length commonly used by anglers.
• TOS - Terms of Service. These are the rules we must agree to follow to become and remain members of this site.
• UGF - Under Gravel Filter
• UGJ - Under Gravel Jets
• W/D - Wet/Dry filter.
• YGM - You've Got Mail (The person sent you an email message. A reference to AOL's annoying voice that tells you when you have mail.)
• YGPM - You've Got Private Message
• YMMV - Your Mileage May Vary (This worked for me. It may or may not work for you.)