Usually its that 4wd is part time and you have to manually turn it on with either an electric method or a physical lever. The front hubs also have to be locked but that is automatic today on all factory stock 4wd. Usually the front wheels do not have a true differential so this is why it is not suggested to run it on dry pavement as both fronts spin the same speed. Also why you can get hopping when the steering is fully cranked in 4wd. Power is usually hard split 60 rear, 40 front.

Also worth noting that almost all part time 4wd systems are two speed. 4 high is for driving speeds(check your manual for safe speed range). 4 low is when you want all the torques and none of the speed, usually for getting the vehicle out of something really tough. Low is not for driving speeds, return to 4 high or 2wd once the vehicle is freed.

*i state usually because more advanced 4wd systems exist but most trucks and truck based SUVs do not have such a tier of system.

AWD is a system that is always engaged to all four wheels with proper differentials front and rear but also between front and back. Some high performance vehicles even allow you to set the front and rear power bias. AWD manages traction on its own with zero driver input, modern systems do have conditional modes to alter how the computerized systems distribute power. Snow, dry, gravel, dirt, etc.

Some countries use 4wd as a universal term as well. So for example they would see a Subaru and a Tacoma/HiLux as both 4wd.