A rondeau in professional kitchens is a large wide bottom pot different from a stock pot in that it is much wider than it is tall.
The wide surface area of a rondeau allows for maximum evaporation during cooking and allows for a higher volume of food to have direct contact with the pan's hot surface during cooking. Converse this with a stock pot whose smaller base and higher side are more conducive to moist heat cooking over longer periods of time with more minimal evaporation.
Rondeaus are great for searing large format meats and high volumes of smaller cuts of meat and vegetablea. For instance you will need a rondeau to sear a side of pork belly, or sear off a large number of veal shanks. Both items are going to be braissd so anything where you are searing the proteins, sweating out the vegetsbles, pinçaging, and deglazing are best started in a rondeau and then transferred into a hotel pan, cartouched, and put into the oven at a low temperature. Clams and mussels can be steamed opened in a rondeau, and nuts can be browned.
Rondeaus work decently on a range of burners but be mindful that the heat will be unsaved as they tyoicallu cover up multie burners. To prevent scorching, regularly rotate the rondeau so the portion directly over a burner doesn't get too hot. French tops, with their concentric rings of heat are a better match for rondeaus when available.
It's best to work with a towel in one hand using it to push and pull the rondeau while stirring with a spatula or a pair of tongs in the other hand.
If you find yourself needing more surface area, a steam table may be a bettter option.