The umbrella term for block, strap, bolster and blanket. They bring the floor up to you instead of forcing you into a crooked pose – arm extensions, not a weakness.
The most stubborn beginner myth is that props are for inflexible people. They're actually a measuring instrument. A block under your hand brings the floor up to you in a forward fold, so you can hinge from the hip instead of rounding your back – and because it has three heights, it works like a training weight: start high, lower it over the weeks, read your progress off the block rather than off a feeling. The strap does the same job for your arms, the bolster opens the chest, the blanket tilts a stiff pelvis into an upright seat. The usual mistake is fetching them only once a pose already pulls – by then you're stuck in a compromise. Lay them out beside the mat first.