Step 1: Understanding the Concept:
Sexually Transmitted Diseases (STDs) or Infections (STIs) are infections that are primarily spread through sexual contact.
Step 2: Detailed Explanation:
There are viral, bacterial, and fungal STDs.
Common examples include:
1. AIDS (Acquired Immunodeficiency Syndrome), caused by the HIV virus.
2. Syphilis, caused by the bacterium \textit{Treponema pallidum}.
3. Gonorrhea, caused by the bacterium \textit{Neisseria gonorrhoeae}.
Step 3: Final Answer:
Two examples are AIDS and Syphilis.