What does it mean to add an interface after a variable in the go language?

Title just started to learn the go language some do not understand:

a.Data = make(map[string]interface{})

I think it is in the application of a. Data map is a string type of space, then it is followed by an empty interface what does it mean?

What does it mean to add an interface after a variable in the go language? >> Golang

The answer is quite clear:
What does the Http://www.goodpm.net/postreply/golang/1010000008853468/go language mean by adding an interface to a variable. html

What does it mean to add an interface after a variable in the go language?