quota
also: disk quota, user quota, group quota
A system limit that controls the maximum amount of disk space or number of files a user or group can use on a filesystem.
Disk quotas are administrative controls that prevent users from consuming unlimited storage on shared systems. They can be set per-user or per-group, and typically limit either disk space (in blocks) or the number of files (inodes) that can be created.
Linux quota systems support both soft limits (warnings issued, but usage allowed to continue) and hard limits (usage cannot exceed this threshold). When a user approaches their soft limit, the system generates warnings; the hard limit acts as an absolute ceiling.
Example: you might set a soft limit of 1 GB and hard limit of 1.2 GB for a user. The user gets warnings when crossing 1 GB, but the system prevents any writes once 1.2 GB is reached. Quotas are managed with commands like quota, setquota, and repquota.