1/1 means full twist, and 1 1/2 means 1.5 twist. So 1/2 would mean half twist. For example: FX - Strother - back 1½ front 1/1 Thomas... whip to 2½ to front ½... ended with 3/1 (1-step)..."precise routine"
This means back 1.5 twist to full twisting Thomas, whips to back 2.5 twist to punch Barani (front half), back triple twist.
Most twists (especially ones with more than one twist) is done in layout position, so if not specified, assume if it's done in layout position.
Few other common terms: tucked full-in means double tuck with full twist on the first salto. Full-out would mean double salto with twist on the second salto. Half-in Half-out means half twist in first salto, then another half twist in second salto. Laid out 1/1 out means double layout full-out. Rudi means front 1.5 twist, and Randi means front 2/5 twist.
HTH