Not all sectionals are symmetrical. Some are quite longer on one side than the other. Sometimes it would be handy for the chaise to be on the opposite side.
Thankfully there is a uniform way our suppliers use to refer to which side is which.
Imagine standing in the middle of the room and looking AT your sectional. If the chaise is on your left then it is a left side chaise sectional like the brown one below.
The opposite would be a "right side chaise" sectional
Some sectionals come with an armless chair which can be inserted. We have to think about those carefully. Consider Ashley's venerable Alenya sectional. It can be made longer on the right or left side by putting the LOVESEAT on the side you would like to be longer and the sofa on the shorter side
Here is an overhead outline of the Alenya with the long side on the RIGHT SIDE when facing it.: