This is a heavier, bolder variant of the cursive script style — same flowing letterforms, with more visual weight so it stands out further against a busy background.
Standard Unicode script characters are thin and can be hard to read at small sizes; the bold script block was defined separately with thicker strokes, giving a result that stays legible in tighter spaces like a username.
Unlike regular script — which substitutes a handful of letters with older lookalike symbols — bold script was defined completely, so every letter follows the same consistent pattern.
Bold cursive shows up most in display names and short bio lines where a decorative, higher-weight signature look is the goal.
Generally yes, since the added stroke weight helps the flowing shapes stay distinct even at small sizes.
No — Unicode doesn't define a bold script number set, so digits pass through unchanged.
Yes — convert only the portion you want styled and paste it into the middle of your normal sentence.