Mode has several different meanings:

1. A way or manner of doing something. When your teacher asks you to switch from reading mode to listening mode, she's asking you to change how you're working. A phone in airplane mode operates differently than normal. Scientists might say that a machine operates in different modes depending on what task it needs to perform.
2. In mathematics, the mode is the number that appears most often in a set of data. If you surveyed your class about how many pets everyone has, and five kids said “two pets” while everyone else gave different answers, then two would be the mode. It's useful for finding what's most common or typical in a group of numbers.
3. In music, a mode is a type of scale with a particular pattern of notes. Musicians use different modes to create different moods and feelings in their compositions. Medieval church music relied heavily on modes, and many folk songs still use them today.

Whether you're talking about a mode of transportation (like walking versus driving) or the mode in a math problem, you're describing a particular way something works or is done.