Is oral sex safer than real sex? Can I still get an STD from it? What is the difference between an STD and an STI?

Oral sex is not any safer than sexual intercourse when it comes to getting STDs.  The most common STD spread through oral sex is Herpes.  STDs can be transmitted through bodily fluids, such as blood, semen, and vaginal fluids.
 
The terms “STI” or sexually transmitted infection and “STD” or sexually transmitted disease mean the same thing.  “STI” is a more common term now because it fights the stigma that the word “disease” in “STD” brings.
 
For more information about STDs
https://www.teensincharge.org/topics/sexual-health/sexually-transmitted-diseases-stds/
 
 References:   
http://www.mayoclinic.org/diseases-conditions/sexually-transmitted-diseases-stds/in-depth/std-symptoms/art-20047081
http://www.cdc.gov/std/