What is the main difference between PATCH and PUT request?

Put :
if i want to change myfirst name then send put request for Update

{ "first": "Nazmul", "last": "hasan" } 

but here has one problem is put request that when i want to send put request i have to send all two parameters that is first and last
so it is mandatory to send all value again

Patch :
patch request says . only send the data which one you want to update and it won't effecting or changing other data .
so no need to send all value again . just i want to update my first name so i need to send only first name to update .