Definitions for soapbox
Random House Webster's College Dictionary
or soap′ box`
an improvised platform, as one on a street, from which a speaker delivers an informal speech or political harangue.
Origin of soapbox:
a crate for packing soap
dais, podium, pulpit, rostrum, ambo, stump, soapbox(noun)
a platform raised above the surrounding level to give prominence to the person on it
A crate for packing soap, or, by extension, any inexpensive crude platform raised above the surrounding level to give prominence to the person on it, especially when used for speeches.
The madman obtained a soapbox which he stood on at the corner of Broadway and Wall street, to shout out his prophesy of the end of the world.
A talk about one's pet topic (or the topic itself), especially when only tangentially relevant to an ongoing discussion.
He's been on his soapbox all day about the new football coach.
a soapbox car
To give a speech from (or as if from) a soapbox.