That can be classified as a "want". Wants and needs are prevalent notions through people's lives. Needs are minimum requirements to stay alive(I need air, water, food to live) and go throughout one's day(clothing and transportation to go to work), and wants are extra icing on top that makes a person feel good(fart apps), whatever that might be. The trouble is people that people sometimes get the two confused.. that's where fart app makers win.

Is Angry Birds something I 'need?' Well, maybe for some people I guess.

Cheaper than therapy ;) Though arguably one could classify entertainment as a need.