>>501083Shoujo = younger girls. Famous shoujo magazines are Lala, CocoHana, Ribbon.
Josei = adult women. Famous josei magazines are You, Office You, Comic Zero Sum, Aria.
Shounen - younger boys. The most famous is Weekly Shounen Jump, but you also have Weekly Shounen Magazine, Weekly Shounen Sunday, etc. They are the most popular demography and not only younger boys read them.
Seinen = adult men. Popular magazines are Kirara, Young Animal, Ultra Jump, Young Jump etc.
Just because it's published in a magazine aimed for a specific target audience doesn't mean it won't attract a public with different tastes. For example, despite Banana Fish being a shoujo, it was extremely popular with older men, and despite K-On being a seinen, it was extremely popular with younger girls.
