Single Journey Visit Visa

Hi,
I have received a Single Journey Visit Visa Valid for 21 days Stay in Hong Kong valid for 3 months (Indian Passport holder with an unsuccessful PAR request). As I am coming for Various Trade shows and will be traveling from Hong Kong to China 3-4 times between a period of 10 days I would like to know how many times can I re-enter Hong Kong.

it also says a maximum time of stay 21 days on Each landing, the wordings are very confusing any help will be grateful.
Thanks.