What does 'read' mean in add_theme_page(); ?

I am trying to add a Theme options page, and this is the piece of code i am using..

add_theme_page('Theme Options', 'Theme Options', 'read', 'theme-option-slug' , 'theme_settings_page');

I am wondering what does the ‘read’ in the list of parameters mean. Also, If I replace it with Administrator, it does not work.

What all values Can I use to replace the ‘read’. I read on WordPress CodeX, it is the field for Capability. But, entering options like ‘Editor’, Administrator, etc in the function does not work.

So, I need to know the exact value of the code I can use….