Definitions of rant on the Web:
harangue: a loud bombastic declamation expressed with strong emotion
bombast: pompous or pretentious talk or writing
talk in a noisy, excited, or declamatory manner
wordnet.princeton.edu/perl/webwn
A rant is a widespread and distinctive phenomenon of emotional speech or writing usually consisting of complaints or attacks, sometimes in a political nature. Rarely, rants express great praise, defending an idea or a person from attack.
en.wikipedia.org/wiki/Rant