Variables can be used to declare some values which remain constant throughout the template. The value of the variable once calculated does not change. Variables can be either simple strings or DSL helper functions. If the variable is a helper function, it is enclosed in double-curly brackets {{<expression>}}. Variables are declared at template level. Example variables - 
variables:
  a1: "test" # A string variable
  a2: "{{to_lower(rand_base(5))}}" # A DSL function variable
Currently, dns, http, headless and network protocols support variables. Example of templates with variables - 
# Variable example using HTTP requests
id: variables-example

info:
  name: Variables Example
  author: pdteam
  severity: info

variables:
  a1: "value"
  a2: "{{base64('hello')}}"

http:
  - raw:
      - |
        GET / HTTP/1.1
        Host: {{FQDN}}
        Test: {{a1}}
        Another: {{a2}}
    stop-at-first-match: true
    matchers-condition: or
    matchers:
      - type: word
        words: 
          - "value"
          - "aGVsbG8="

# Variable example for network requests
id: variables-example

info:
  name: Variables Example
  author: pdteam
  severity: info

variables:
  a1: "PING"
  a2: "{{base64('hello')}}"

tcp:
  - host: 
      - "{{Hostname}}"
    inputs:
      - data: "{{a1}}"
    read-size: 8
    matchers:
      - type: word
        part: data
        words:
          - "{{a2}}"