As electronic communication (email, chat, sms, mms) becomes more and more pervasive in our world, users of English as a second language are also beginning to use acronyms on a frequent basis.
Here are some of the most popular ones:
FAQ Frequently Asked Question
TIA Thanks in advance
IMO In my opinion
CU See you
FYI For your information
BTW By the way
LOL Laughing out loud
RU are you
And there are many, many more. The important thing is that you keep in mind that these acronyms are to be used for business friendly or informal situations. In other words, don't use them for very formal communication.
For more information, you may also check out this very complete Acronym List on the web. There you will find a very extensive list, some formal, some informal.
Acronyms are almost a way of life in English speaking countries. So just for fun, here's a video that tells a silly little story with acronyms. Watch it and see how many you know... and how many you don't? Enjoy!