To let up means to become less intense, to ease off, or to stop pressing so hard. When a rainstorm lets up, it weakens from a downpour to a drizzle. When your soccer coach finally lets up during practice, she gives you a water break after running drill after drill.

The phrase suggests a reduction in pressure or intensity. A strict teacher might let up a bit before the holidays, assigning less homework than usual. If you've been studying for hours, your parents might tell you to let up and take a break. When someone says “don't let up now,” they're urging you to keep going with the same effort, not to ease off when you're close to finishing something important.

You can also ask someone to let up on you, meaning you want them to stop criticizing or pressuring you so much. If your older brother keeps teasing you, you might say, “Let up already!” The phrase captures that feeling of relief when something difficult or overwhelming finally becomes more manageable.