A text message is a short written note sent from one phone to another. A hundred and sixty characters, originally.
That limit came from the technical space left over in the mobile network's signalling channel, which is why texts were free for operators to carry and enormously profitable to sell. The first one was sent in 1992 and said merry Christmas. It is usually shortened to a text, which is also the verb. Messaging apps have largely replaced it except for banks and delivery drivers.
1nountext messageA short written message sent between mobile phones.
“She sent a text message from the platform.”