An mow is a sound that grass makes when it's cut with a machine. The word can also be an action of cutting or trimming something like grass.
When you need to keep your lawn looking neat and tidy, you often have to mow it. This usually involves driving a big machine around your yard, turning the blades on as you go, so they chop up the tall blades of grass right down to size. Some people prefer to mow their lawns themselves, while others hire someone else to do it for them.
The act of mowing (a garden, grass etc.)
Example: The lawn hasn't had a mow for a couple of months, so it's like a jungle out there!
To cut down grass or crops.
Example: He mowed the lawn every few weeks in the summer.
