What does “k” mean in a text?

What it most likely means

Okay. Usually typed fast by someone busy, walking or driving. People who are upset tend to write more, not less.

What six different Brads heard

Everyone has a Brad: the anxious little security guard in your head. Six of them read “k” and every one of them is sure. None of them have evidence.

The Archivist · Division of EvidenceLast week they wrote 'okay!!' with two exclamation points. The exclamation points have been withdrawn.
The Proofreader · Division of Outgoing MessagesOne letter. We sent four sentences. They were clearly the wrong four sentences.
The Volume Officer · Division of DimmingWe sent too much. They answered with the smallest possible amount of alphabet.
The Fire Marshal · Division of ExitsOne letter is how goodbyes start. Brad has located the car keys.
Customer Service · Division of Keeping Everyone HappyThey are upset with us. Apology drafted. Offense unknown. Draft six.
The Forecaster · Division of Worst-Case WeatherOne letter. Civilizations have ended over less.

Perfect. Talk later!

Great. Text me when you're free.

k means ok