If you say Y here, you will be able to set per user limits for disk
usage (also called disk quotas). Currently, it works for the
ext2, ext3, and reiserfs file system. ext3 also supports journalled
quotas for which you don't need to run quotacheck(8) after an unclean
shutdown.
For further details, read the Quota mini-HOWTO, available from
<http://www.tldp.org/docs.html#howto>, or the documentation provided
with the quota tools. Probably the quota support is only useful for
multi user systems. If unsure, say N.

source code:

fs/quota/dquot.c