Information is in transmission when it flows from one location to another, usually over some medium such as network cables, wifi, or audio waves.
The transmission of data and information is happening constantly. The internet wouldn’t be possible without data transmission. When data is on the move, it is known as “data in motion,” and when it is not moving, it is known as “data in rest.” These days, it’s just as important to secure data in motion as it is to secure data at rest. The process for securing each kind of data is related, but different. For example, encryption is used to secure both kinds of data, but the way that encryption keys and created and implemented is usually different.