be under pressure

1. Literally, to be compressed within some vessel with great force. The contents of this container are under pressure, so do not pierce it or expose it to fire or you could risk triggering an explosion. Crude oil underneath the ground is usually under intense pressure, which is why it can erupt into a geyser if a deposit is struck. That spray paint is in an aerosol can because it needs to be under pressure.

2. To be facing or enduring a great amount of stress caused by some compelling or constraining influence. I can't talk now, I'm under pressure to get this done before the end of the day! Sorry, I'm just under so much pressure at work that it's made me rather irritable. We've emptied our life savings into our company, so we're definitely under pressure to make it successful.