This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. The act or an instance of calling back from one location or situation to the previous one: a callback of laid-off auto workers.

n. A return telephone or radio call.

n. A recall of a recently sold product by the manufacturer to correct a defect.

n. The return of a situation to a previous position or state.

n. A return telephone or radio call; especially one made automatically to authenticate a logon to a computer network

n. A product recall because of a defect or safety concern.

n. A function pointer passed to another function that the latter can call for notification purposes.

n. a follow-up audition (casting)

n. a joke which references an earlier joke in the same routine

"Your callback will be used within the main form, so you must not include any tags or a form submit button. register_widget_control ($name, $callback [, $width [, $height]]);"

call    send for    respond    answer    reply   

recognise    brush up    recognize    know    refresh   

string    chelation    asynchronous    input/output    mechanization