Clout is slang for respect, reputation, etc.. It's often used by rappers in their songs to remind everyone they have respect from their peers(criminals) and even some of their enemies. Having clout means that you are likely feared in the streets due to your reputation and you have taken actions to earn that respect. Having clout also means you have so type of fame, since people will know you.
In L'A Capone's song So Loud he says "These boys ain’t got no clout", he's simply implying that his enemies have no reputation/fame. Fly Boy Gang, a rap group from Chicago have adopted the nickname Clout Boyz.