Please refer to the above-mentioned PHP manual link for a complete description.
The search provider to get stats on (ask/bing/clearch/duckduckgo/google/yahoo/yandex).
The format for numbers, the options are i18n (uses the format of the current country as set in WordPress), English (uses 1,000.00 style formats) or none (the default will return n number without any formatting)
The page/post ID to get statistics on. Only used on page visits.
The “stat” field can be any of the followings:
The number of users online right now.
The number of hits to the site.
The number of visitors to the site.
The number of times the current page has been visited