1) Proofreading device 2) Typo-detecting program 
In computing, a spell checker (or spell check) is an application program that flags words in a document that may not be spelled correctly. Spell checkers may be stand-alone, capable of operating on a block of text, or as part of a larger application, such as a word processor, email client, electronic dictionary, or search engine. It came with my P...
An application feature that users rely on to correct their grammar. The de facto industry standard requires the Spell Checker's dictionary to contain all the words in the English language except computer terminology and competing vendor's product names. 
[n] - an electronic dictionary in a word processor that can be used to catch misspelled words
spelling checker noun an electronic dictionary in a word processor that can be used to catch misspelled words