A keyword search searches for exact word when a boolean search looks for synonym's.

The difference between a keyword search and a boolean search is the focus of the search. A keyword search is a search for an exact word. A boolean search is a search for a synonym.

Keyword search is finding the most desirable keyword for your website while directory search is finding relevant directories where you can submit your website.

Doing a keyword search online.

conduct a keyword search in search engines and online encyclopedias.

(site traffic of keyword) / (search volume for #1 result for keyword) * 100% = SoV

There is no limit for Google's keyword search as long as you are not doing it by means any automation.