1.
( informal ) used to tell sb to wait or stop
SYN wait :
Hold on a minute while I get my breath back.
Hold on! This isn't the right road.
2.
to survive in a difficult or dangerous situation :
They managed to hold on until help arrived.
3.
( informal ) used on the telephone to ask sb to wait until they can talk to the person they want :
Can you hold on? I'll see if he's here.