A person of Polish descent, within the meaning of Act, is a person who declares Polish nationality and fulfills all the following conditions:
1. at least one of his/her parents or grandparents or two great grandparents were of Polish nationality,
2. he/she demonstrates its relationship with Poland, in particular by cultivating Polish language, traditions and customs
Yes, Polish descent, not Polish citizen - you can't get citizenship through your grandparent, it would be possible only if one of your parents have/had Polish citizenship.
But still you may apply for permanent residency in Poland.
The person whose Polish origin has been confirmed in accordance with statute may settle on Polish territory permanently.