A lot of people think an emo is a suicidal person who holes out in their room, planning their death, writing poetry and songs, and cutting. Those same people also think that people who don't do all those things, but still say they're emo are "emo posers." And while there is a such thing as emos and emo posers, those are the stereotypical descriptions, not the real ones.
There are no rules that say specifically "to be emo, you must do this." Emo is a style, although many people in this day's society use it as a label, kind of like how we call people who are smart nerds or geeks.
The emo style has no rules as well. You don't absolutely have to have the fringe over your eyes, your hair dyed black, red, blue, or some random color. You don't have to cut yourself, you don't have to be suicidal or depressed. Really the main thing that makes up the emo style is the music and the appreciation of it.
Some people might be into the type of music classified as emo or punk, but wouldn't appear to be emo on the outside. They may like the style of clothing, they may call themselves emo, but that doesn't automatically mean they're suicidal and depressed.
If they are sucidal, depressed, or if they cut, they tend to hide that from others. It's as if its their deepest secret; they don't want others to know about it. They may tell their closest friend or sibling, but they certainly do not prance around school saying "EVERYBODY LOOK! I CUT MYSELF! ISN'T THAT GREAT?"
The real emo style is basically you being free with yourself. Some stereotypes are true, or at least partially true, and others are not true at all.
Emo posers are very different from regular emos. They're the kids to wish to be emo, but don't seem to fit any of the stereotypical requirements, so they force themselves to. Emo posers usually follow every single stereotype. They may willingly cut themselves, then show it to others, complaining how their horrible life made them break under pressure. They claim that they're suicidal and depressed, but in reality their life will most likely be fine.
Emo posers try their hardest to be emo, but in the end they epically fail. Some people just aren't made to be emo, so trust your instincts.