WordPress multisite is when you one to run multiple WordPress sites but do not want to have to update multiple versions of each WordPress sites when there are updates. How multisite works is that you install WordPress only once and configure it to allow multiple sites to be created within the one code base.
in the background this is what happens when configured:
On a normal install of WordPress when the site is created at first the site uses the whole database with each table having the same table prefix (ex. wp01_) what you see in red specifies that it is that database which is configured for that site which is configured in the wpconfig.php file.
After WordPress multisite is configured for each additional site that you create there are new tables that are created with new table prefixes example:
Site 1 – wp01_
Site 2 – wp01_2_
Site 3 – wp01_3_
Now what you see in “blue” are the new database tables that are created for the new sites also know as “blogID”. This method allows WordPress to create multiple tables inside one database with ever numerical value in the blue section being assigned only to that specific new site.
Now you might wonder why would I use WordPress Multisite? Well to tell you the truth Multisite is only good to use for certain things. If you plan on creating a site that deals in general with the same niche market or same business type just different locations or branches then WordPress Multiste would suit your needs.
When installed it makes it easier to mange multiple sites with one single login and one location. Sounds great doesn’t it! there is only only one thing. When it comes to WordPress Multisite maintenance and trouble shooting you have to have some experience in this as it is not an easy task. This is why WordPress Multisite is not recommended for the novice.
WordPress multisite also makes it easier to manage all your plugins and themes for all your sites from one location. One thing to keep in mind when selecting plugins for WordPress multisite be very careful as not all plugins work well with WordPress Multisite and when installed and activated can bring down your site. It is always good to do your research as to the compatibility of plugins when it comes to Multisite.
Depending on the project you are working on and the amount of site you might have the basic WordPress multisite should fit your needs. Remember you have multiple WordPress sites or blogs running on one code base and a single database. In this case your one point of failure can be the database. WordPress Multisite it self is rock solid, the introduction of plugins add code to WordPress and sometimes make DB changes and this is what can make it a point of failure. To solve the database problem and to provide for growth there is the option of doing “MultiDB” with WordPress Multisite. This though is not for your average person. It is not that technically hard to implement if you are familiar with certain terms and can follow directions but it just adds a whole new level of maintenance. This is usually used by big companies with thousands of sites.
If this is something that you need and you are a beginner we would suggest that you work with someone that has experience on this so that they can help you get Multisite setup and provide you with ongoing support in case needed. A perfect example of a WordPress Multisite and MultiDB would be WordPress.com They provide free WordPress sites and blogs to users. All of their sites are running on one code base with multiple databases supporting it.