What is the data type of Multiselect field if I fetch it using API?

What is the data type of Multiselect field if I fetch it using API?

I have multi select (pick list) field like this




and let say in deal record I picked several options (20 ft and 45 ft) like this



my question is, what is the data type of it if I fetch it using Restful API? is it a String in JSON ?
  1. {
  2.    "Container" : <What data type in here>,
  3. }