The yum search command will display information about a package in the repositories you have installed, regardless if the package is or is not installed on the system. The repositories you have installed will be listed at the beginning of the output. It is very common to install the EPEL (Extra Packages for Enterprise Linux) repository.

~]$ yum list | head
 * base: centos.mirrors.tds.net
 * centos-sclo-rh: mirror.den01.meanservers.net
 * centos-sclo-sclo: mirror.den01.meanservers.net
 * epel: mirror.team-cymru.com
 * extras: centos.mirrors.tds.net
 * updates: mirror.genesishosting.com

In this example, information about the httpd package is displayed.

yum search httpd
. . .
Loaded plugins: fastestmirror
Repodata is over 2 weeks old. Install yum-cron? Or run: yum makecache fast
Determing fastest mirrors * base: mirror.es.its.nyu.edu * 
extras: mirrors.gigenet.com * 
updates: mirror.nexcess.net
====================================== N/S matches: httpd =================
libmicrohttpd-devel.i686 : Development files for libmicrohttpd
libmicrohttpd-devel.x86_64 : Development files for libmicrohttpd
libmicrohttpd-doc.noarch : Documentation for libmicrohttpd
httpd.x86_64 : Apache HTTP Server
httpd-devel.x86_64 : Development interfaces for the Apache HTTP server

Similarly, the yum info command can be used to display information about a package.

yum info httpd
. . .
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirror.oss.ou.edu
 * centos-sclo-rh: sjc.edge.kernel.org
 * centos-sclo-sclo: mirrors.usinternet.com
 * extras: linux-mirrors.fnal.gov
 * updates: mirror.atlanticmetro.net
Available Packages
Name        : httpd
Arch        : x86_64
Version     : 2.4.6
Release     : 90.el7.centos
Size        : 2.7 M
Repo        : base/7/x86_64
Summary     : Apache HTTP Server
URL         : http://httpd.apache.org/
License     : ASL 2.0
Description : The Apache HTTP Server is a powerful, efficient, and extensible
            : web server.