While most instruments produce notes at concert pitch, transposing instruments produce a note that is different to the one that is written. For example, two common orchestral transposing instruments are clarinet in B♭ and horn in F.
When a clarinet in B♭ plays a C, the sound produced is a B♭, one whole step (tone) below. When a horn in F plays a C, the sound produced is an F, a fifth below. Other instruments that conventionally produce a pitch different to the one notated include the piccolo (sounding an octave above written), double bass (sounding an octave below written), and glockenspiel (sounding two octaves above written).
Dorico Pro stores all note information in concert pitch and automatically transposes notes as appropriate for the transposition of the instrument. This means notes, key signatures, and chord symbols are automatically changed in transposing layouts compared to non-transposing layouts. You can also change instruments at any time, and the music is adjusted automatically to ensure the correct pitches are shown.
You can also change the octave of individual clefs and whether Dorico Pro respects or ignores clef octave indicators in each flow independently.
Additionally, you can override the clef and/or transposition in each layout independently.