Think of a piano which is an instrument in the key of C. Using the same reasoning, if you play a C major scale on an E flat instrument, you will be playing the Concert E flat scale. Therefore you are playing CONCERT B flat scale. If you play a C major scale on that B flat instrument, it will sound the same as the B Flat scale on a piano or other C instrument. Think of an instrument in the key of B flat such as a euphonium or a cornet. A Concert F is the F on a piano or guitar. A Concert C is the C on a piano or guitar. The phrase Concert B flat means the pitch or sound produced if you play a B flat on an instrument that is in the key of C, such as a piano or a guitar. You have to convert their notes (transpose) to play the same sound/pitch. That's because instruments are made in different keys. The C on a piano is not the same as the C on a trumpet. not every instrument plays the same sound. You may wonder what it means when an instrument is, for example, a B flat instrument? Well. The Difference Between E Flat & B Flat Instruments, etc.

C and e flats