LOL = laugh out loud, in the modern internet understanding. I'm not sure what you mean by LO, unless you mean a shortened version of "hello": 'lo. In older texts, "lo!" is used dramatically, to mean something like "voila!" (there! see! here it is!). "And lo! there was much rejoicing." You'll also find it used in the expression "lo and behold".

lo means Used to draw attention to an interesting or amazing event. something like LOOK! or SEE! LOL means many laughs, laughing audibly, laughing in a loud voice(Internet Slang) You can use it when you find something funny. for example, you write it on one of your friends post on facebook or something like that.

Good comments all. Thank you very much!

I'm not sure about the "LO"... where have you heard this? "LOL" stands for "laugh out loud", which you probably already know, and it is used online when you find something funny. For eg: A friend might have posted this on Facebook: "What do sea monsters eat? Fish and ships." (just using a crappy joke for an example) Then you would reply: "LOL" --because you think it's funny :)