From the WordPress codex here is what level 0 to 10 means. These are presets generate by WordPress that you can use to give your client access to different capabilities with one click:
User Level 0 converts to Subscriber User Level 1 converts to Contributor User Level 2 converts to Author User Level 3 converts to Editor User Level 4 converts to Editor User Level 5 converts to Editor User Level 6 converts to Editor User Level 7 converts to Editor User Level 8 converts to Administrator User Level 9 converts to Administrator User Level 10 converts to Administrator
