Activity Monitor - Dock Icon - dual core is displayed with 4 columns View > Dock Icon has two CPU choices:


Show CPU Activity
Show CPU History


I am on a dual core (MacBook Air (13-inch, Early 2014).
In both views, I see 4 items.

Using High Sierra.
While researching the Activity Monitor, I saw this:

Some of the newer Macs have hyper-threading, which makes each core appear to be two processors.

Relatively speaking, I'm less familiar with hyper-threading than older CPU technology, so I'm putting this in an answer, and letting the community vote.