The Peek Definition displays the definition of the selected element in a window without navigating away from your current location in the code editor. It lets you preview the definition of a type without leaving your current location.
The Peek Definition and Go To Definition are almost similar, the only difference is that Peek Definition shows the information in a pop-up window, and Go To Definition shows the information in a separate code window.
Let's right-click on the member name and choosing Peek Definition from the right-click menu.
You will see that the member definition is opened up in the popup window.
The definition window appears below the line that contains the member in the original file. The window doesn't hide any of the code in your original file.
X) button on the definition window tab.
You can open another Peek Definition window inside an already open Peek Definition window. A set of breadcrumb dots appears next to the definition window tab, which you can use to navigate between definition windows.
The tooltip on each dot shows the file name that the dot represents.
The CTRL + Click will run the Go To Definition command, but you can make it open a Peek Definition window by changing an option on Tools > Options > Text Editor > General.
Check the option Open definition in peek view and click OK button. Press Ctrl and click the member, you will see the Peek Definition window instead of Go To Definition.