Estery: It is the aroma and/or flavor of any ester (fruits, fruit flavorings, or roses). I like a few banana notes with my wheat beers but too much of anything is undesirable. The usual culprit is poor temperature control. Each yeast has different thermal sensitivity. The same yeast can give clove flavors at low temperatures but banana/fruity notes at high temperatures. Maintaining lower and constant temperatures is the key to keep them manageable.
However, isolating the contribution of the fruity notes from the fruits/ flowers/ hops and that from the yeast cannot be done without access to the recipe. Making tea from the ingredients is the first step towards understanding these notes before altering the fermentation temperature conditioning.