Client level 0 – 10

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 
You can read more about WordPress’s roles and capabilities here:  https://wordpress.org/support/article/roles-and-capabilities/