1Grandfather — a polite or affectionate term for one's own or someone else's grandfather.
おじいさんの家に夏休みに遊びに行った。
I went to visit my grandfather's house during summer vacation.
お祖父さんは昔から魚釣りが得意だ。
Grandpa has been good at fishing since long ago.
おじいさんは毎朝早く起きて庭の手入れをしている。
My grandfather gets up early every morning to tend the garden.
2An old man; a male senior citizen — used to refer to elderly men (not necessarily one's grandfather).
公園でおじいさんたちが将棋を指していた。
Old men in the park were playing shogi.
バスで席を譲ってほしいと、若者におじいさんが頼んだ。
An old man asked a young person on the bus to give up a seat.
駅でおじいさんが道に迷っていたので、案内した。
An old man was lost at the station, so I helped guide him.