What is "Google Suggest" or "Autocomplete"?

"Google suggest" is the name of Google's auto-complete function. If a user enters a letter or a word in Google's search field, they are automatically shown associated terms in a drop down menu.  This function helps users save time and may also provide them with additional information about the topic they are researching.
"Autocomplete" is a feature in which an application predicts the rest of a word a user is typing.
Hope it helps you...

Google's Auto-suggest is an algorithm by Google to provide better user experience in choosing from the search term(as suggested by Google) that the users are looking for.

The auto suggest is a feature which suggest keywords from the popular searches that has/had happened in Google. The word to notice here is "POPULAR".

Google Suggest is an attribute of Google search engine. Google suggest notably speeds up the search process and surely makes search experience better. It restricts users programmatically pull its autocomplete suggestions.

Google Suggest is the name of Google's auto-complete function. If a user enters a letter or a word in Google's search field, they are automatically shown associated terms in a dropdown menu. These suggestions are generated based on the most frequently searched terms.

provide better user experience for choosing the search term that the users are looking for.
autocmplete  suggest is a feature which suggest keywords from the popular searches that had happened in Google.
The word to notice here is "popular"