What's going on: I got nothing when many applicants got rejection from the same grad program I am an applicant of a biology graduate program. After exploring some on a website, the gradcafe.com, I found that I got nothing when many applicants got rejection on a specific day from the same graduate program. Several waves of invitation were alread gone now, but I got neither invitation nor rejection. 

Do you think it's a good sign? I don't know much about how graduate admission process is going on. Could you a bit explain this situation?

PS. I asked about it by an email to the office of the grad program, but they didn't answer yet even after 5 days. No phone number available...
The only people who know are involved with the admissions process. Maybe they have accepted you, but just have sent the acceptances out or maybe they rejected you and you rejection is in a later batch. They also could have never received or lost your application. You just cannot know. In a situation like this, where you think something is up because other people have heard, it would be inappropriate to ask the admissions team what is happening. If you think they lost your application, and if they sent you an aknonowledgement it is very unlikely, then it might be reasonable to ask. Then again, it is pretty late to check and they are probably not interested in getting a late application.

In simple terms, not having been rejected yet is much better news than having been rejected. Not having been rejected when others have, is not particularly predictive.