If a sound is voiced, the vocal cords are vibrating and producing a noise.

If a sound is voiceless (or 'unvoiced'), the vocal cords are not vibrating or producing a noise.

Also called  lead-in or starter. It is theintroductory stage of a lesson - usually an introduction to the topic and/or target language of the lesson you are about to give.

See open questions.

It is a group of related words that all have the same root (or 'base form') - e.g., happiness, happy, unhappy,happily. 

See main stress.