It can be bundled with Application and Database Development tools like Visual Studio or embedded with an application that needs local databases. LocalDB is a lightweight version of Express that has all its programmability features, yet runs in user mode and has a fast, zero-configuration installation and short list of pre-requisites.
This will take time to download, meanwhile let's see briefly what are other editions of SQL Server 2014 Express.
During this, I encountered minor road blocks, which I overcame to install SQL Server Express 2014. I had planned installation of SQL Server Express 2014 on Windows 10 PRO OS.