If I had to explain to my grandmother what messenger is in simple words, I would say that it is a program for users to communicate with each other. Messages are sent almost instantaneously. The applications are developed by different companies and are installed on a computer or smartphone. Depending on the functionality of each of the programs in them you can simply exchange text messages (like SMS), add pictures - stickers to your correspondence, send files in different formats, communicate in groups or even make video calls with one or more people. I use
Softgoza and it is one of the versions of WhatsApp. I don't know how I would explain it to her. LOL.