What is the meaning of Trump's 'thumb-and-index-pinch' when he speaks? When Donald Trump speaks in front of a crowd, he often puts his hand at shoulder level, usually far from it, and lets his palm face the crowd and pinches his thumb and index together while either closing the other fingers or keeping them all straight.

What does that gesture mean?
Short answer
The 'OK pinch' (Fig. 1) expresses precision and control. It stresses particular phrases and shows commitment to his words.

Background
In an interview with Psychology professor Geoffrey Beattie, communication specialist Alan Stevens addressed this point on Euro News:


source: Euro News  


  ...This is probably Trump’s most well-recognized gesture – the OK
  pinch between the thumb and forefinger. [It] helps him show precision
  and control.  
  
  These batonic [Not representing anything specific] movements are stressing those bits of the message that he sees as important [...]. In some sense it’s showing commitment to what he’s saying[,] but what he’s also doing is adding an extra layer of subconscious meaning.”



Fig. 1. Hand gestures. The second shows the thumb and forefinger touch. source: Fred Hatt