What is the usage of backtick in golang structs definition? [duplicate]

This question already has an answer here:

type NetworkInterface struct {
    Gateway              string `json:"gateway"`
    IPAddress            string `json:"ip"`
    IPPrefixLen          int    `json:"ip_prefix_len"`
    MacAddress           string `json:"mac"`
    ...
}

I’m quite confused what’s the function of contents in backtick, like json:"gateway" .

Is it just comment, like //this is the gateway ?