From a scientific point of view, the classification of many fruits as "fruit" or "vegetable" is a tricky business. There are a multitude of definitions and for some plants even technically experienced botanists still do not agree whether it is a fruit or a vegetable. The avocado is also a tricky case.
The avocado is a berry
While most people would automatically classify this tropical fruit as a vegetable, from a botanical perspective it's more of a fruit. The perennial avocado tree belongs to the laurel family and its fruits are therefore assigned to the berries. So the correct answer is: The avocado is a berry and therefore a fruit.
tips and tricks
The avocado is rich in an essential, unsaturated fatty acid and therefore very healthy. However, only enjoy the pulp when it is raw, as it becomes bitter and inedible as a result of heating it up through boiling or frying.