Ichimi-togarashi (cayenne pepper powder) is a seasoning made of dried red pepper ground into powder form. It's used to add a sharp flavor to various dishes.
In the Kanto region it's also called 'Ogara,' 'Okara' and 'Okkara.'
Meanwhile, Shichimi-togarashi (a mixture of red cayenne pepper and other aromatic spices) can be classified as a different seasoning from Ichimi-togarashi, because it's a compound of Ichimi-togarashi and other spices. However, both seasonings are often confused because they're similarly used as condiments for dishes such as udon (Japanese wheat noodle) and because the names "Ichimi" and "Shichimi" sound similar. Unlike Shichimi-togarashi (literally, cayenne pepper powder with seven flavors), Ichimi-togarashi is composed solely of red pepper, and therefore it's called "Ichimi-togarashi" (literally, pure cayenne pepper powder).
As mentioned above, Ichimi-togarashi is generally used as a condiment for dishes such as udon. However, unlike Shichimi-togarashi, Ichimi-togarashi is composed solely of red pepper, and therefore Ichimi-togarashi is an appropriate spice not only for Japanese food but also for Western foods such as pizza and curry, which it enhances with a sharp flavor.