LOL

• "LOL," short for "laughing out loud," is among the most commonly used abbreviations for laughing. The choice of lowercase or capital letters in this abbreviation also indicates the degree of laughter. Used in instant messages, emails and texts, "LOL" also appears regularly on social networking sites. This abbreviation for laughing has become so widely used that it's been referred to on nationally televised programs.
  
  

LMAO

• "LMAO" is used to indicate hard laughter and stands for "laughing my a** off." The more polite version of this abbreviation is "LMBO" ("laughing my butt off" or "laughing my backside off"). "LMAO" or "LMBO" reflects strong laughter or something that's funnier than the more traditional "LOL" would indicate.
  
  

ROTFLMAO

• "ROTFLMAO" or "ROFLMAO" is short for "rolling on the floor, laughing my a** off." This abbreviation reflects laughter that's harder or lasts longer than a laugh indicated by the abbreviations of "LOL" or "LMAO." This particular abbreviation for laughing has become so widely used that certain role-playing games have turned the abbreviation into a word and used it in songs featured on the game's website.
  
  

SWL

• "SWL, or "screaming with laughter" is used to indicate the maximum hilarity and laughter. When people write "SWL," they're likely doing a full belly laugh that includes knee slapping. This particular abbreviation for laughter isn't as widely recognized or used as "LOL," "LMAO" or "ROTFLMAO" and seems to be used in spurts before it fades back out of use again.