PRONUNCIATION ------------------------------------- ←
chunk 81: phonetics jargon
→ pronunciation guide anusvAra visarga
The "puff" after stops .
position is the part of the mouth that obstructs the air most.
Openness is the distance between the parts of the mouth that most obstruct the air.
" Velar " means back of tongue near back of palate
" palatal " means middle of tongue near roof of palate
curledback means "tongue curled back".
Dental means tongue tip hits teeth.
"labial" means lips approach each other
The twenty stops of Sanskrit are pronounced with some puff of air. Technically explained: during stop consonants like t th p ph ph k kh, the tongue or lips stop completely the pass of air. While the obstruction lasts, the pressure behind the obstruction rises, and when the obstruction is released some air goes out in a burst. The hissing sound made by that air I call a " puff". In Wikipedia on https://en.wikipedia.org/wiki/Aspirated consonant aspirated consonants, you can read how to test for the presence of a puff using a candle flame.
Ancient Sanskrit grammarians call that puff a prANa ("air"). They say there are two sorts of stops. The ones with "small air" are called alpaprANa, they are --
k g c j T D t d p b
And the ones with "big air" are called mahAprANa --
kh gh ch jh Th Dh th dh ph bh
The k g etc are pronounced in exactly the same way as the kh gh etc, the only difference being that the ones written with fake h accumulate more presure, so that when the obstruction is released, the puff is noisier.
See also hints to learn to pronounce the puff .
Openness is the distance between the parts of the mouth that most obstruct the air.mmmmmmmmm
^ C+ 1418 
Example. The letters t, s and i all are made by moving the tongue tip somewhat near the teeth. In all three, tongue and teeth obstruct or disturb the pass of air. Therefore their position is the same, dental.
Yet, in t the pass of air is fully closed and no sound gets out, in s it is almost closed and there is hissing, and in i the pass is open. Therefore these sounds have different openness.
pANini says that t s i have different prayatna, "effort". The idea here is that saying t needs more tongue pressure than saying s, and s more pressure than i.
Similarly, all of b F v u are labial, but the lips have different degrees of openness: closed, almost closed, a bit open, open.
curledback means "tongue curled back".mmmmmmmmm
^ M- C+ 1421 
" curledback" is the position of the tongue when saying S and the five Tu. When saying the curledback letters, the tongue curls backward. These letters are also known by many other funny names such as retroflexes and cerebrals; in Sanskrit they are called mUrdhanya "made with the top". The word is used in the rule a-padAntasya mUrdhanyaH "replace non wordfinal with curledback".
Even though the letters R RR r S do not curl so far back as Tu, they do curl somehow, so grammarians toss those into the curledback group anyway. There is, however, a very important difference between the Tu and the S R RR r --
When saying T Th D Dh N the tongue hits the palate and comes inmediately back down,
but after S R RR r, the tongue stays half-raised after hitting, and will stay somehow raised until some other letter makes it go back down.
Bengali speakers beware: the tongue does NOT stay raised after you say N. Instead, it works exactly like Bengali D. Practise that by chanting --
kaJM cit kAlaM sa dharmAtmA sItayA lakSmaNena ca
In the N, the tongue moves down instantly. It is lakSmaNena, not lakSmaNeNa !
PRONUNCIATION ------------------------------------- ←
chunk 81: phonetics jargon
→ pronunciation guide anusvAra visarga