[146] [h]: voiceless glottal fricative
This is the ‘h’ sound of English, German and other languages (in French, however, for example, the ‘h’ is mute and is never pronounced at all). It is the simplest sound of all: just breathe out through your mouth (without letting your vocal cords vibrate). In other words, it is a pure (voiceless) aspiration.
Although it is classified as a fricative, it would make just as much sense to consider it as an approximant (but a voiceless one, which is strange), because you don't really constrict your vocal cords beyond the normal amount of frication that goes on in the laryngeal region anyway.