Overflow means to spill over the edges of a container because there's too much to fit inside. When you fill a glass with water and keep pouring, the water overflows onto the counter. When a river gets too much rain, it can overflow its banks and flood the surrounding land.

The word can describe physical things spilling out, but it also describes feelings or situations that become too big to contain. A classroom might overflow with excited energy before winter break. Your heart might overflow with gratitude when someone does something incredibly kind for you. A stadium overflows with fans when every seat is taken and people are still trying to get in.

In computer programming, an overflow error happens when a program tries to store a number too large for the space available, like trying to write a 20-digit number in a spot designed for only 10 digits. The number “overflows” its designated space, which can cause problems.

Notice how overflow suggests abundance, sometimes wonderful (overflowing with joy) and sometimes problematic (an overflowing toilet). The key idea is always the same: there's more of something than the space can hold.