'massive' is an adjective. a massive object denotes a large one, typically larger than normal. It can often be used to exaggerate size and/or scope.
only applicable to physical objects, not abstract concepts (e.g. using 'massive' to describe an idea or goal). Can be intensify an already existing adjective (e.g. replacing 'big' with 'massive'), but cannot be used to describe someone's skill or ability (e.g. can't replace 'good' with 'massive').
1. The ancient tree had a massive trunk.
2. The investigation uncovered a massive fraud.
3. The lake had a massive fish that weighed over 100 pounds.
it is important to remember that the word massive generally relates to physical objects and has no place outside of this context. Because it is an adjective used to imply an exaggeration of size, you should avoid attaching 'massive' to things that are already considered large (such as mountains or oceans).