"Gymnastics" is generally referenced to gymnastics *skill* training that does not require significant amounts of energy to do such as say forward rolls, backward rolls, cartwheels, roundoffs, handstand balance work, and then starting to get into routine type stuff on the events specifically like the actual skills you would perform in a competion like giants with pirouetting and stuff on high bar, circles and various techniques on pommel horse, etc. It's always best to do this when fresh because that's when skills are best ingrained neurologically. You don't want to do them after strength or metcon because you'll be tired and usually that's when bad habits or poor technique is performed leading to poor neural patterns ingrained in your muscle memory.
ME gymnastics type stuff is pure strength work like working towards a back lever, front lever, planche, iron cross, inverted cross, maltese, etc.
metcon can utilize gymnastics exercises combined together usually in circuit fashion. So Mary, JT, 30 MUs for time, etc. are all relatively decent gymnastics-ish metcons.