An inode is basically a file - so say you had 1,000 images, that'd be 1,000 inodes. Every file (a webpage, image file, email, etc) on your account uses up 1 inode
Shared servers only support 50,000 files. You may slightly exceed this limit, but we will not continue to create automatic backups. It will be a problem if you continuously publish and delete large numbers of files, like 10,000 at a time.
It will be a problem if you are in excess of 150,000 files. Please refer to section 26.1) of our Conditions of Use
You can read more about inodes here:
http://en.wikipedia.org/wiki/Inode