If you need to query the package database and you do not have network connection with the enabled repositories, you may use the -C to only search on the local cache. The data in the cache must be up to date and the required action must not imply a download from the network. Simple example of a package search:
$ yum -C search squid
...
================================ Matched: squid ================================
lightsquid.noarch : Light, small, and fast log analyzer for squid proxy
lightsquid-apache.noarch : Web Controls for lightsquid
squid.x86_64 : The Squid proxy caching server
squidGuard.x86_64 : Filter, redirector and access controller plugin for squid
calamaris.noarch : Squid native log format (NLF) analyzer and report generator
awstats.noarch : Advanced Web Statistics
ccze.x86_64 : A robust log colorizer
dansguardian.x86_64 : Content filtering web proxy
mod_auth_ntlm_winbind.x86_64 : NTLM authentication for the Apache web server
: using winbind daemon
tinyproxy.x86_64 : A small, efficient HTTP/SSL proxy daemon
