For all levels: In Tenniscores, the abbreviation FRZ (frozen) means that a player is not available to play. The captain oversees this function and can utilize it to identify players that are not available for an extended period of time. See How to do a Frozen player?

FRZ (frozen) for a 5.0 or 5.5 player (level 1):  a 5.0 or 5.5 player can only be labelled as "FRZ" if she is unable to play for at least 8 matches. This player can only be labelled "FRZ" once per season. 
A notice of 7 days must be given before a player can be added to or removed from the FRZ list. (AGA2017)
The captain must inform her statistician before declaring a player frozen in Tenniscores.