I explained about Onbu and Onbuhimo to a mom who lives in the Southern Hemisphere.

Hi, thank you for your question. You would like to know the recent definition of onbu and what exactly proper onbuhimo is, wouldn’t you?
There is no definition of onbu, but I can say following things according to several documents:

・A baby is on the high back of the caregiver, and can see the same direction as the caregiver.
・The position in which a baby can move both arms as they like is called onbu.


The act of doing Onbu has a meaning.

“Onbuhimo” is a tool for achieving these points, made of fabric. There are hard-structure-type baby carriers used for onbu, and we call them “shoiko”.
There is no definition of onbu, and originally old Japanese people applied common long cloth. Because Japanese people wore kimono, they had various width and length of cloth (himo) in their house.
That’s why there is no definition of onbu, and a tool mode of fabric for achieving the position stated previously is called “onbuhimo”.

Onbu's philosophy is about to be forgotten in Japan.

But, nowadays a lot of structure-type babycarrires are manufactured. They are also called “onbuhimo”, but they cannot achieve the position. There are only few people who remember the onbu in the past days, so I think most of contemporary Japanese interpret “ a tool for keeping a baby on the back = onbuhimo”.
In my opinion, following actions could significantly damage profits that baby can get from onbu:

     A baby should be on the low position and they cannot see anything over the caregiver’s shoulders. ( an obstruction of joint attention)
     A baby cannot move their arms as they like. There is a gap between caregiver’s back and a baby because of insufficient closeness. ( an obstruction of inflowing of information through sense of touch, intention of passive posture) 
     A baby cannot move the legs under the knees as they want and cannot cling to a caregiver. ( the loss of chance of motor development)

that's all. Please send me a message if you have more questions.