What is a Label in Compiler Speak?

A Label identifies a location in source code.

This takes the form of an identifier, often followed by a punctuation character, e.g. colon.

There are various examples:

Function labels, switch statements have various case labels, common lisp has something of the form:

(let ((iteration NIL))
  (tagbody
    start
      (print 'started)
      (setf  iteration 0)
    increase
      (print iteration)
      (incf  iteration 1)
      (go    check)
    check
      (if (>= iteration 10)
        (go end)
        (go increase))
    end
      (print 'done)))

Where tagbody creates a scope, where labels are define as forms starting with a symbol.