マイブーム literally means a boom of my own, and a Japanese writer called Miura Jun made it up. If you say "アボカドがマイブームです", that means "I'm really into avocados just for now" or "I'm obsessed with avocados". Although this word was chosen as a catch phrase in 1997, people seem to feel it is getting outdated. It's even appeared on a book about dead languages. I myself haven't heard this word recently.

『マイブーム』は、自分の中の流行です。 自分が集めていたり、お気に入りのもののことを言います！ 『italkで言語を学ぶことがマイブー ムです』といった感じです☆