The 'approach path' to a shrine. It is used for the path from the first torii to the centre of the shrine but may be extended also to roads leading to the shrine. Technically the sando should not follow a straight line, perhaps because it was thought disrespectful or inauspicious to approach the kami directly, but in many shrines circumstances dictate that the sando is straight. The term gives rise to street names linked to shrines such as omote-sando, the 'front approach'.
A Popular Dictionary of Shinto. Brian Bocking.