What is Friedel–Crafts reactions?

A Friedel–Crafts alkylation attaches an alkyl group to an aromatic ring from a halogenoalkane and a Lewis acid ($\ce{AlCl3}$). A Friedel–Crafts acylation attaches an acyl group $\ce{RCO}$ from an acyl chloride and $\ce{AlCl3}$, through the acylium ion $\ce{R-C#O+}$, giving an aryl ketone.