A Retention

1. The act of retaining or something retained
2. The act or power of remembering things
3. A memory; what is retained in the mind
4. (medicine) The involuntary withholding of urine and faeces
5. (medicine) The length of time an individual remains in treatment
6. (obsolete) That which contains something, as a tablet; a means of preserving impressions.
7. (obsolete) The act of withholding; restraint; reserve.
8. (obsolete) A place of custody or confinement.
9. (law) The right to withhold a debt, or of retaining property until a debt due to the person claiming the right is duly paid; a lien.