This is a 1950s (maybe late 1940s) vintage tuxedo tails aka a formal tailcoat.  These vintage tuxedo tails are made in classic form with padded shoulders, chest pocket, no closure, cut away front with six buttons, two buttons at the back and a single button at either cuff.  It has black satin peaked lapels.  It is fully lined in black satin viscose and the exterior fabric is a lightweight black worsted wool.  Note that there are no pants included, only the vintage tuxedo tails.
Label: Label has been removed
Sizing: There is no size label on these tails and although these should fit a medium size (US 40), please rely on the following measurements for fit, taken from the exterior (please take the thickness of the fabric into consideration):
Shoulders: 19” across shoulder seam-to-seam
Sleeves: 25” from shoulder seam
Sleeve Inseam: 17 1/2” long
Chest: 43” around (21 1/2” across pit-to-pit), taken under the arms with a normal gap - note that suit jacket sizes are normally 3”-4” smaller than chest measurement
Waist: 39”-40” around, with a normal gap
Overall length: 43“ at the back, measured flat from the neck seam
Condition: These vintage tuxedo tails are in very good condition with no pronounced wear, tear or staining - it looks like it saw little use and was well stored over the years.  
These are nice vintage tuxedo tails  - with a proper pressing, they’ll look great!