Means string expression and is either:

• a string, for example:
  
  • "3"
  • "Test 3"
• an expression that will result into a string, for example:
  
  • "Test " + "3"
  • "Test " + STR$(3)
  • "Test " + b$, with b$ = "3" or b$ = STR$(3)
• a parameter that has a string as value, for example:
• b$, with b$ = "3" or b$ = STR$(3)

See also Quaestor Syntax