i want to know the actual definition for the term tafkheem and tarqeeq, some books write it as full mouth and empty mouth.

Question
Assalamu alaikum

i want to know the actual definition for the term tafkheem and tarqeeq. some book writes it as full mouth and empty mouth, from what i've been taught was heavy and light.i also know that mukhaffam is full mouth, muraqqaq is empty mouth. i am confused.
please do state the actual meaning!!!
jazakallah

Answer
The actual correct English term for tafkheem (which an Arabic word written in English transliteration) is velarization.  This is the term used for letters that are pronounced so that the back of the tongue raises up and the sound is focused up to the roof of the mouth and there is an echo like sound caused from this.  The correct English term for tarqeeq is attenuation.  This is the opposite of velarization, the tongue does not raise up and the sound is not focused up to the roof of the mouth and there is no echo sound. These terms though, would be found in linguistic books, not in every day conversation.

We do not know why some use the term full mouth and empty mouth for tafkheem and tarqeeq.  Heavy and light kind of give an indication of the sound, so can be used.  We tend to use the Arabic terms. 
Wa iyyaakum.