What is a prolonged blast?

Rules of the Road.
Rule 32. Sound & light Signals
Definitions
(B) The Term "short blast" means a blast about one seconds duration.
(c) The Term "prolonged blast" means a blast of four to six seconds duration.

Rule 34 Maneuvering and Warning Signals

International. (a)One Short blast means "I am altering my course to starboard" (right)
Inland. (a) One Short blast means "I intend to leave you on port side" (left)