Priority date is the date when a principal applicant first reveals his or her intent of immigration to the US government.

If you are a prospective immigrant, you can find your priority date on Form I-797, Notice of Action, for the petition filed on your behalf. The waiting time before receiving an immigrant visa or adjusting status depends on:

• The demand for and supply of immigrant visas.
• The per-country visa limitations.
• The number of visas allocated for your preference category.

Some foreign nationals (typically Indians, Chinese etc.) cannot file for adjustment of status (using form I-485) after the application for alien worker is approved (I-140) but must check that their priority dates are current

No it is not only for Ph.D’s. The requirement for advanced degree for the EB2-NIW application is a baccalaureate or foreign equivalent degree plus 5 years of post-baccalaureate, progressive work experience in the field

This is by far the most important question when considering applying for the EB2-NIW application. You may be eligible for an employment-based, second preference visa if you are a member of the professions holding an advanced degree or its equivalent, or a foreign national who has exceptional ability. Here’s an article that will help you make that decision.

You are welcome to discuss any aspect of your EB2-NIW application until the allotted time is up. 

The decision to approve or deny your application rests with USCIS.