4hi is 4wheel drive, but without the center diff locked, so the front and rear wheels are able to spin independently of each other, like AWD cars such as Subaru's, etc. This means you can drive it on pavement without the driveline binding, like it would in locked 4wd.

I use the term AWD to differentiate (pun intended <img src="/forums/images/graemlins/lol.gif" alt="" /> ) between 4HI, and 4HLC.

1991 HZJ77, 1999 KZJ90, 1999 UZJ100, 1992 M101CDN2
https://www.thegearheadproject.com/category/jdm-journeys/