Inverted Cross: A gymnastics skill performed on the still rings.  It is an inverted handstand position, with the arms stretched straight out from the shoulders perpendicular to the body. Essentially it is an upside-down iron cross. 

Inward turn: A gymnastics or ballet turn on the feet (foot) in the opposite direction of the supporting leg.  In other words, if a gymnast does a traditional full turn on the left leg turning it to the left, an inward turn is done on the same leg and turns to the right.   Inward turns are also known as reverse turns. See also Full Turn. 

Isometric Muscle Contraction: An isometric muscle contraction  when your muscle contracts, but does not change in length. A common example of an isometric muscle contraction is hanging from a chin-up bar with your arms bent at 90 degrees. In this case the bicep muscle contracts, but does not change in length because you're not moving up or down.  Examples in gymnastics would include and iron cross An example is any static hold (L sit, iron cross, etc) 

Iron Cross: A strength move performed on the still rings, in a straight body or " L" position, with the body perpendicular to the floor and the arms stretched straight out perpendicular to the body. 

Isometric Stretching: Isometric stretching is a type of static stretching (meaning it does not involve motion) which involves the resistance of muscle groups through isometric contraction of the stretched muscles.. The use of isometric stretching is one of the fastest ways to develop increased static-passive flexibility and is much more effective than either passive stretching or active stretching alone. Isometric stretches also help to develop strength in the tensed muscles (which helps to develop static-active flexibility), and seems to decrease the amount of pain usually associated with stretching.  The most common ways to provide the needed resistance for an isometric stretch are to apply resistance manually to one's own limbs, to have a partner apply the resistance, or to use an apparatus such as a wall (or the floor) to provide resistance. 
 

Gymnastics Dictionary