To run into somebody is to meet them by pure chance. Neither of you planned it and there they were.
It is used constantly about acquaintances, so running into an old colleague in a supermarket is the standard scene. Bump into does the same job. There are two other senses: running into a wall or a car is a collision, and running into difficulties or into debt means encountering them. A fourth use is about numbers, since costs can run into millions.
1phraserun intoTo meet someone unexpectedly.
“You might run into her at the market on Saturday.”
2phraseencounterTo encounter a problem, or to collide with something.
“They will run into trouble if the weather turns.”
Also accepted in games: bump into
Practised in Phrasal Verbs, A Man Called Ove
First appears in chapter 3 of A Man Called Ove.
Practise this word