||A kurta is basically a long tunic or shirt. Traditionally,
it is a panel garment much like a caftan with sleeves. No fabric
is wasted, and gussets are placed in possible stress points. That
probably isn't a strict requirement anymore though, since there are now
many styles of kurta.
A kurta is usually mid thigh to knee length. This is comfortable in hot weather, warm in cold weather, and in Muslim societies, fulfils the requirement of modesty for men. Yes, men have requirements too, and form fitting garments shouldn't be worn in non related mixed company unless it's necessary. It's considered very shameful for a woman to see the shape of a man's private parts, so many Muslim men wear kurta to protect them from this.
A kurti is a shorter version of the kurta that, nowadays, is often worn by women. The short version of a men's kurta is called a panjabi, and this is sometimes worn with dhoti, a draped version of shorts.