Thanks for the question. You will find a few answers here, including discussions of canonical freedom, so check the labels (canonical freedom, etc.) to the right as well. Simply put, canonical freedom means one is free to undertake the rights and obligations of a public (canonical) commitment. This might be freedom to marry, freedom to make a religious profession or to be consecrated, or freedom to receive or be admitted to certain other sacraments like Orders.
In terms of religious profession and consecration, canonical freedom implies not merely the ability to meet physical, material, and mental standards of the vocation, but more fundamentally, it means the presence of a faith history of having received all the sacraments of initiation and Confirmation, and also the absence of bonds of sacramental marriage or (if one is looking to marry instead) bonds of religious consecration and/or ordination which must be dispensed. If one has been married sacramentally then either the spouse must be deceased, or, if the couple divorced, the Church must have granted a decree of nullity (which says there was never a sacramental bond created in the first place) before one is considered canonically free to undertake another life bond. All of these events are noted in one's Church of Baptism with one's baptismal record and are also recorded in the place where they occurred. A diocese, seminary, or religious congregation will require this record before proceeding with plans to allow one's entrance into any process of discernment or formation and will keep their own personal file for the person applying.
What the Church teaches is that when one makes a whole-hearted commitment of the entirety of one's self and life in marriage, religious life, consecrated virginity, or priesthood, one is no longer free to dispose of oneself in the same way in another state of life. The commitment one makes originally (and subsequently if free to do so) announces that God has called one to become a whole and holy human being through this specific path. It underscores not merely the importance of life commitments but also the significance of the discernment any vocation requires.Catholic theology regards freedom as the power to be the persons we are called to be. Canonical freedom indicates freedom in law to respond to God's unique call to become whole and holy in, with, and through Him in a particular state of life. If one is not canonically free, one cannot even begin to discern or pursue a given vocational path. It has taken some centuries for the Church to honor Sacramental marriage appropriately by not allowing married persons to run off to a monastery or hermit cave, for instance, or simply to live as brother and sister while eschewing sexual or marital love, but that is the emphasis today. Today the Church esteems married life and marital love more adequately so canonical freedom cannot so easily be achieved by dispensations instead of the necessary decree of nullity. I sincerely hope this is helpful!