1
general::
Rise to speak formally to an assembled group, as in After that long introduction, the treasurer took the floor. This idiom uses floor in the sense of "right to speak," in turn derived from its meaning as the part of the legislature from which members address the group. [c. 1800]
American Heritage Idioms
2
general::
Phrase(s): take the floor
1. Fig. to stand up and address the audience. • When I take the floor, I’ll make a short speech. • The last time you had the floor, you talked for an hour. 2. Fig. to go to the dance floor in order to dance. • They took the floor for the foxtrot. • When the band played, everyone took the floor.
McGrawhill's American Idioms And Phrasal Verbs