A morning coat (also known as a cutaway) is a coat designed as a slightly less formal coat for men to wear in the morning before having to wear a traditional dress coat or other dress item.
While the morning coat started as a formal day wear alternative to the frock coat, it quickly gained popularity to the point where it was considered an acceptable option for full on formal dress. At the height of their popularity it was acceptable to wear a morning coat to all manner of social events from weddings to formal gatherings.
A traditional morning coat is single breasted, with the front joining at a single button located at the middle of the coat. The two sides then gradually sweep back (below the button) to form tails that land well above the knee. So, the morning coat is a somewhat 'informal' type of tailcoat jacket. The morning coat traditionally was constructed with a double breasted lapel, though this is not an absolute necessity. The morning coat is commonly worn in combination of an ascot tie while the tailcoat is worn with a bow tie.
While it was originally created as a semi-casual alternative to the more formal dress coat, the morning coat is almost exclusively worn as a piece of formal dress in modern times as the majority of people no longer have to dress formally on a day to day basis.