From The TV IV
Shōjo is a genre of Japanese animation and comics (anime and manga) targeted at a young female audience (shōjo means 'young girl'). Stories for an older female audience are sometimes called josei, though it is not unusual to see the term shōjo encompass female stories for all ages.
On the creative side, shōjo is usually created by females for other females. But it is not uncommon for many shōjo creators to be male, as well as many fans to be male. Like any other artistic genre, it comes down to personal preference.
There are many things unique or special about shōjo that distinguishes it from its male counterpart shōnen (which means 'young boy' and therefore caters to same), far beyond the gender of the protagonist. While many shōjo titles feature female heroines, there are also some shōjo titles starring guys (who more often not are extremely attractive). The proliferation of attractive male leads in shōjo even forms its own subgenre – bishōnen ('pretty boy').
If the creators, audience, and main character are not female, how do we know if a program is shōjo? It depends on style. Shōjo finds it closest Western equivalent in the romance genre, which is generally accepted to be aimed toward a female audience. While men may fall in love as well, most male stories with a romantic bent usually find themselves shelved in the contemporary fiction or even erotica sections. A shōjo anime or manga need not focus on romance, but often do. Romances present a prime example of the emotional conflicts that permeate shōjo works, with action and other external concerns often taking a backseat to internal struggles.
These conflicts do not always involve romance, and sometimes revolve around issues like friendship, school, or family. Relationship troubles are the most common scenario.
Internal struggle is usually joined by some external situation that must be dealt with, forming the standard plots that are often used to describe the show and lend it structure. Unlike shōnen which is about the main action and plot, in shōjo these scenarios are used to develop the characters and progress their relationships.