A Plenary Indulgence...
May be gained (under the usual conditions) when the Rosary is prayed in Church, in a family group or in a religious community. Also:
Five (5) decades of the Rosary must be prayed continuously.
The prayers of the Rosary must be prayed vocally and one must meditate upon the Mysteries of the Rosary.
If the recitation of the Rosary is public, the Mysteries of the Rosary must be announced.
A Partial Indulgence...
One may gain a partial indulgence for the Rosary's recitation in whole or in part in other circumstances.
A Plenary Indulgence...can be gained only once a day (except by those who are in danger of death.)
To gain a plenary indulgence one must perform the indulgenced act. Three other conditions must be fulfilled:
1. A sacramental confession
2. Eucharistic Communion
3. Prayers for the intentions of the Church
In addition, one must be free of all attachments to sin, even venial sin. If this complete integrity is not present or if the above conditions are not fulfilled the indulgence is only partial. Both a plenary and partial indulgence may be applied to the dead.