Memes

Yes but not only, small business owners, small landlords and "casual traders" who own some stocks but not enough to be considered rich or have influence in the company the stocks are from are also part of the petty bourgeoisie.

Generally, the petty bourgeoisie are peoples who technically own means of productions and may even have a few employee working for them, but don't make quite enough from that to not have to work anymore. They are constantly under the threat of being out-competed by larger businesses, especially corporations owned by the high bourgeoisie, and becoming a proletarian.

Basically, they are the subclass at the boundary between the bourgeoisie and the proletariat. They are better off than the proletariat and own means of production and private property but are under constant threat to lose these privileges and become part of the proletariat, especially in time of crisis.

They are the source of the overwhelming majority of fascists as I've said, because they still benefit from capitalism and generally aspire to become part of the high bourgeoisie even tough they are very much the underdogs. The bourgeois state will intentionally let fascism grow unopposed so that if the bourgeoisie feels their privileges are threatened by working class movements, they can give power to the fascists who will crackdown on the proletariat and protect the capitalist system from being overthrown.