A flat is a symbol at the beginning of the staff which indicates the names of the lines and spaces where the note is intended to be a half step lower than the line would otherwise indicate. A sharp would be half a step higher than the line would indicate. For instance, if your register has a flat symbol on the line that indicates a B should be played it means that the composer intended the note to be 1/2 step lower than the pitch perfect B, in other words the composer wanted a B flat played, not a B.
when someone is flat in music it means they're singing in a lower pitch than they are supposed to
One half step below the note. In other words; to go from D to C would be a whole step, to go from D to D flat would be a half step.
The music gets louder
slowly!
Slow
pianissimo!
In musical terms, rinforzando means reinforced.
That's not a standard term in music.
Play loudly!
Bb is B flat as typed on a keyboard.
It means "smooth and connected".
A style or music is simply a characteristic that sets it apart from other types of music.
Tab is a form of music that many guitar players read.