Inodes are simply the amount of individual files in your domain. For example a file that is 1 megabyte or 100 megabytes is still just 1 inode. To speed up your site all your need to do is keep these your files a s low as possible. The more Inodes you have the harder the server has to work to fin a file. The server will have to search your whole domain for each file that is loaded.
The account soft limit is 150k, that is a 150k total files. More than that and we will have to do a custom set up to handle more files.
You can speed up your website easily by removing emails or running your email off site.
Another good trick is to have a couple separate websites and have some files hot linked on separate accounts.
The official definition is:
Data structures that contain information about files in Unix file systems that are created when a file system is created. Each file has an inode and is identified by an inode number (i-number) in the file system where it resides. inodes provide important information on files such as user and group ownership, access mode (read, write, execute permissions) and type.
There are a set number of inodes, which indicates the maximum number of files the system can hold.
A file’s inode number can be found using the ls -i command, while the ls -l command will retrieve inode information.