1A sudden feeling of surprise or astonishment; used as an adverb or with suru to indicate being startled or amazed.
彼の突然の訪問にびっくりした。
I was surprised by his sudden visit.
子供が大声を出して、犬がびっくりして逃げた。
The child shouted, and the dog was startled and ran away.
あの商品の値段はびっくりするほど安かった。
The price of that product was surprisingly low.
2A noun meaning a surprise itself or something intended to surprise (e.g., a surprise party).
友達が誕生日に内緒でびっくりパーティーを開いてくれた。
My friends secretly threw me a surprise party for my birthday.
あの知らせはみんなにとって大きなびっくりだった。
That news was a big surprise to everyone.