I've always understood it to be that 'type-ahead' is a category that includes both autocomplete and autosuggest. Those two are subtly but importantly different.

I've always understood it to be that 'type-ahead' is a category that includes both autocomplete and autosuggest. Those two are subtly but importantly different. As 'suggested' by the name, autosuggest acts somewhat like a recommendation engine. It takes the characters that have already been typed, and uses those to search for potentially related keywords, etc., even if those don't match the literal characters the user has typed. Autocomplete, meanwhile, is a 'dumb' tool that enables things like tab-complete. Both are considered flavors of type-ahead.